* add trailing commas on list/map/parameters

* add trailing commas on Invocation with nb of arg>1

* add commas for widget containing widgets

* add trailing commas if instantiation contains trailing comma

* revert bad change

* the onStart callback will report the location of the pointer where it wins the gesture arena by default instead of the pointer down location. Fixes all tests related to changing this default value.

This reverts commit 08538f91.

* Adds start behavior option to the drag gesture recognizer and makes it the default option when a drag gesture recognizer is created. Also fixes all the tests to work correctly with the new default behavior.

* enable lint unnecessary_new

* fix tests

* fix tests

* fix tests

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.

This is not a grand refactor yet, it's just cleaning up what we have
already, so that people who keep using this API (e.g. dialogs) have
something coherent to deal with.

The major changes are that Navigator and NavigatorState have the same
API now, that most of the examples use `<void>` instead of `<Null>`,
that the navigator observer can see replaces, and that the `settings`
is moved from ModalRoute to Route. I also cleaned up some of the API
documentation.

* replace child parameter with builder on showDialog

* change builder parameter to WidgetBuilder

* mark child as deprecated and expand documentation to cover this and how builder should be used

* tidy comments and address some feedback

* phrasing

* move space to prev line and add //ignore comments for deprecated member use

* address comments and fix it's its

* update code samples

* adds semicolon to code snippets

Fixes #13743 
Fixes #12379
Follow-up to #13745

Also adds an option to hide gestures introduced by `InkWell` and `InkResponse` from the semantics tree (see also `GestureDetector.excludeFromSemantics`).

* Make drawer demo header not scroll

* Add test for gallery drawer demo and fix user accounts drawer header overflow

Previously, we used `Alignment`, which was difficult to understand. Now,
we just use an `Offset` scaled to the child's size, which is much easier
to understand.

Alignment will eventually replace FractionalOffset.

Also includes minor doc fixes.

backgroundColor -> color
backgroundImage -> image
BackgroundImage -> DecorationImage

* more widget const constructors

* prefer const constructors

* address review comments

Aggressively apply the const lint.

* Add cupertino to gallery and add CupertinoButto

* Use single quotes

* Add disabled state

* Some review notes

* Make button animation more responsive and tweak timing

* Renamed things Cupertino

* Button with background, move cupertino demos, move material demos

* Move 2 level list too

* Refactor various demo route names

* Some review notes

* More reviews and add test

* Linter as

* Move private constant up

This prepares us for a CustomScrollView that takes slivers.

This patch deploys ScrollView in a number of demos and manual tests.