Fixes the pattern for some TODOs to match our style guide.

(Also, a couple of minor code order fixes.)

It was causing problems rolling Flutter into Fuchsia

* re-enable lint unnecessary_const

* remove trailling whitespaces

* remove unnecessary const (after merge)

This reverts commit cc1cf13e.

fuchsia_tester.dart still assumes Dart 1. Previously, it ran tests directly
from source, flutter_platform.dart automatically runs a kernel compile when
operating in Dart 2 mode, but this assumes a functional Dart SDK is available
in the artifacts directly, and fuchsia_tester.dart mocks out the artifacts
directory with an empty temp dir.

Remaining work is:
1. Get the frontend server building as a dependency on Fuchsia.
2. Patch fuchsia_tester.dart to use a valid Dart SDK and frontend server.

This also reverts migration to Dart 2 typedef syntax.

This reverts commit 6c56bb24. (#18362)
This reverts commit 3daebd05. (#18316)

Now that Dart 1 is turned off, reapplying my change to turn on the prefer_generic_function_type_aliases analysis option, and fix all the typedefs to Dart 2 preferred syntax.

Also eliminated the unused analysis_options_repo.yaml file and turned on public_member_api_docs in analysys_options.yaml.

No logic changes, just changing the typedef syntax for all typedefs, and updating analysis options.

This fixes #17169 by adding onChangeStart and onChangeEnd to the slider. These will be called when the user starts a change, and when they end a change, regardless of whether that change is a tap or a drag.

These differ from onChanged, in that they only report when the user starts and ends an interaction, not at every slight change.

* Address post-submit comments

* Added dispose protection for the animation controllers.

This adds a slider demo with a custom theme to the gallery.

In the process of adding this, I decided to add a text theme to the SliderThemeData, since it's a pain to change the text style on the value indicator otherwise.

This change makes the discrete slider show the value indicator for a minimum amount of time for any interaction (tap, drag).

Fixed the real repaint problem the Slider had (missing addListener), and added tests for it.

Added GlobalKey reparenting test.

Added the ability for the value indicator to slide left and right to avoid falling off the edge of the screen.
It only shifts as much as it can without deforming, but even at large text scales, that is enough to keep the text on the screen.

Updated the formatting on theme_data.dart and others to use longer line length.

Also, removed a color tween that faded the value indicator in as it scaled, since that wasn't to spec.

Fixes a small rendering problem when dragging the slider, as well as a couple of small bugs (de-duping of value changes, and actually using a parameter passed to _unlerp).

This implements an update to the look of the Slider widget.

Specifically, it does the following:

* Adds the ability to customize the colors of all components of the slider
* Adds the ability to customize the shape of the slider thumb and value indicator
* Adds the ability to show the value indicator on continuous sliders
* Updates the default value indicator to be a "paddle" shape with new animations.
* Changes the tick marks to be visible all the time on discrete sliders
* Fixes a memory leak of an animation controller.
* Removes "thumbOpenAtMin" flag, which is no longer needed, and can be emulated by the
custom thumb shape support. It was not widely used.
* Adds tests for all of the new features.

**This PR contains a breaking API change:**
`SemanticsConfiguration.addAction()` has been removed and replaces by action-specific setters (`onTap`, `onLongPress`, etc.) to take care of the fact that some action handlers (those, who take arguments) have different signatures.

* Oct 12 10:12am

* implicit_semantics_test.dart passes

* refactoring

* works in nice

* minor rename

* more doc comments

* to be explicit check better

* fix test

* ++

* ++

* semantics_9_test (BlockSemantics) and implicit_semantics_test are passing

* doc updates

* tiny refactor

* fix static errors in tests

* fix gesture detector

* ++

* ++

* geometry

* ++

* remove noGeometry

* revert test

* +

* all tests but scrolling/clipping pass

* clipping works

* scrolling halfway

* sliver tests pass

* ALL TESTS PASS

* SemanticsNode changed

* docs and tiny fixes

* card test

* more doc comments

* remove missed print

* more tests

* make test pass on Linux

* remove changes to intellij proj file

* review comments

Make material slider respect textScaleFactor

Fixes #5938

Fixes #11358

* Properly update semantics when Material/Cupertino Slider are disabled

* whitespace fix

* fix style

Add Diagnosticable base class and documentation

Refactor RenderObject.toStringDeep and Widget.toStringDeep code to use DiagnosticsNode.

* adds inactiveColor and showThumb to Slider

* add customizable color and showThumb tests

* remove showThumb, add negative tests

Minor fixes throughout, e.g. removing trailing commas from the end of sample code expressions, changing headings to "sample code" more consistently, removing stale todos, fix typos in a private method name, minor grammar fixes, added some clarifications to CircularProgressIndicator, LinearProgressIndicator, CrossAxisAlignment, added some cross-references to various members, made it slightly clearer that layout algorithms are implementation details.

Clarified "elevation" throughout.

Added docs to InkResponse and InkWell.

Added sample code for: SliverAppBar, Card, ListTile, EdgeInsets, Row, Column, CustomScrollView, ListView, SliverFixedExtentList, and SliverGrid.

Fixes #10317.
Fixes #10316.
Fixes #10267. (sort of, see comment therein)
Fixes #9331. (sort of, see comment therein)
Fixes #9407. (sort of, see comment therein)

Previously it was (arbitrarily?) set to 144.0 pixels wide.

Instead just disable the slider.

Fixes https://github.com/flutter/flutter/issues/10055

* more widget const constructors

* prefer const constructors

* address review comments

* make @immutable const

* fix build

* Manually fix every use of Point.x and Point.y

Some of these were moved to dx/dy, but not all.

* Manually convert uses of the old gradient API

* Remove old reference to Point.

* Mechanical changes

I applied the following at the root of the Flutter repository:

git ls-files -z | xargs -0 sed -i 's/\bPoint[.]origin\b/Offset.zero/g'
git ls-files -z | xargs -0 sed -i 's/\bPoint[.]lerp\b/Offset.lerp/g'
git ls-files -z | xargs -0 sed -i 's/\bnew Point\b/new Offset/g'
git ls-files -z | xargs -0 sed -i 's/\bconst Point\b/const Offset/g'
git ls-files -z | xargs -0 sed -i 's/\bstatic Point /static Offset /g'
git ls-files -z | xargs -0 sed -i 's/\bfinal Point /final Offset /g'
git ls-files -z | xargs -0 sed -i 's/^\( *\)Point /\1Offset /g'
git ls-files -z | xargs -0 sed -i 's/ui[.]Point\b/ui.Offset/g'
git ls-files -z | xargs -0 sed -i 's/(Point\b/(Offset/g'
git ls-files -z | xargs -0 sed -i 's/\([[{,]\) Point\b/\1 Offset/g'
git ls-files -z | xargs -0 sed -i 's/@required Point\b/@required Offset/g'
git ls-files -z | xargs -0 sed -i 's/<Point>/<Offset>/g'
git ls-files -z | xargs -0 sed -i 's/[.]toOffset()//g'
git ls-files -z | xargs -0 sed -i 's/[.]toPoint()//g'
git ls-files -z | xargs -0 sed -i 's/\bshow Point, /show /g'
git ls-files -z | xargs -0 sed -i 's/\bshow Point;/show Offset;/g'

* Mechanical changes - dartdocs

I applied the following at the root of the Flutter repository:

git ls-files -z | xargs -0 sed -i 's/\ba \[Point\]/an [Offset]/g'
git ls-files -z | xargs -0 sed -i 's/\[Point\]/[Offset]/g'

* Further improvements and a test

* Fix minor errors from rebasing...

* Roll engine

Rename State.config to State.widget
Rename State.didUpdateConfig to State.didUpdateWidget
Renamed all State subclasses' local variables named config to something else

* add @required when there's an assert not null

* address review comments