* Add a draggable axis restrictor and tests

Take into account the subtitle height when adjusting the height of the widget. Added a test.

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.

Before this change, if you specified a non-null textTheme, but the theme you specified didn't have a body2 defined, then creating a ChipTheme would assert (which means creating a ThemeData would fail).

This adds handling for this corner case to default to reasonable values in that case. The slider had the same problem, but for accentTextTheme, so I fixed that too.

While I had the patient open, Hans and I noticed that TextTheme.merge wasn't doing the right thing in the case where some members were null either, so I fixed that, and added some examples, since merge/copyWith are common operations that are not always well understood.

Fixes #17251

* Allow customization of TextSpan in EditableText

* Addressed PR comments

* Added test with custom-styled EditableText subclass

* More code style fixes

Revert longPress/Tap and Gallery changes

In order to avoid checking binaries into flutter/flutter,
this comparator can be used to retrieve golden files from
a sibling flutter/goldens repository.

https://github.com/flutter/flutter/issues/16859

It allows callers to account for things like shadows that paint
outside the bounds of the widget.

https://github.com/flutter/flutter/issues/16859

See https://github.com/flutter/flutter/pull/15383

* Set text direction in semantics along with Directionality

* update tests for the extra SemanticsNode

New a11y traversal:

- sort direct sibling SemanticsNodes only
- use new sorting algorithm
- implement RTL
- test semantics in traversal order by default
- add AppBar traversal test
- breaking: remove nextNodeId/previousNodeId from the framework
- breaking: remove DebugSemanticsDumpOrder.geometricOrder

When passing a Color object with same R/G/B code ( e.g. [new Color.fromRGBO(100, 100, 100, 1.0)] ) to HSVColor.fromColor(Color color) , the hue in return will be NaN .

As pointed out in the bug, the issue is fixed by just clamping sizeFactor.value.

Fixes #16247 

This adds a toImage function to RenderRepaintBoundary that returns an uncompressed raw image of the RenderRepaintBoundary and its children. A device pixel ratio different from the physical ratio may be specified for the captured image. A value of 1.0 will give an image in logical pixels.

This addresses #16593 by removing the unneeded assert in the setter for constrainedAxis. Null was meant to be allowed there.

This replaces #16599 and fixes #16593, reported by @maksimr

This contains the following commit:

flutter/engine@cb3376c Support different encodings in Image.toByteData() (#16635)

* log error when calling setState in constructor

Semantics object support for edge triggered semantics 

This chip demo is more interactive than the last one, trying to exercise all of the types of chips for a demo that lets you select different types of "chips" (like tortilla, wood, micro, etc.), and then filter them and select an action on them.

* Fine-tune iOS's scroll start feel

* remove negations in doc

* Our own dart-side gesture arena also contributes to the 'jerk'. Make sure that snap is accounted as well.

* Added more code comments from review.

Fixes #14590.