* 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

* a11y: remove SemanticsSortOrder; sort locally only; semanticsOwner post-test check

* update accessibility test framework

- default nextNodeId/previousNodeId to -1
- stop treating null as opt-out from value testing
- add `id`, `TestSemantics.root`, and `tags` to the suggested code in the TestSemantics failure message
- fix a small bug with raw string escaping
- update all tests accordingly

* fix sortKey doc

* prefer const over final

See https://github.com/flutter/flutter/commit/3961306badd313a3f34c5c25a754c1e53a581caf

Updates scaffold to expose bottom padding to the associated
BottonNavigationBar (if present). BottomNavigationBar is now responsible
for adjusting itself to account for bottom padding.

This change is necessary to support the updated BottomNavigationBar
layout for the iPhone X.

This updates the bottom navigation bar to be able to handle more general widgets in the place of the label in the bottom navigation bar, so that Text with a textScaleFactor larger than 1.0 will behave nicely in a bottom navigation bar.

It also means that other widgets given instead of a Text widget for the label will work more predictably.

I also vastly simplified the layout logic, eliminating many computations that were not needed, and refactored the build function to use a separate private navigation tile widget.

Also, the color splash animations were coming from the wrong location (they were coming from far to the right of the touched widget), so that works as specified now.

Move some Cupertino colors to a common file. 

Create a CupertinoTabBar widget to mimic iOS looks

* 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

Aggressively apply the const lint.

Now IconThemeData.fallback is a factory constructor and IconThemeData.of() does
the work of computing the fallback for its clients.

Also, add tests for ImageIcon and ListItems.

* rename DestinationLabel and labels properties to BottomNavigationBarItem and items

* update/fix comments

* grammatical changes

* add myself to AUTHORS

Changed DefaultTextStyle to consider the TextTheme defined in the context for Bottom Nav Bar (#7042)

* Changed DefaultTextStyle to consider the TextTheme defined in the context

* added regression test for bottom nav bar text themes

* added second regression test for fixed navbar