Default `semanticsEnabled` to true for `testWidgets` and fix associated bugs

* Make it easier to ensure semantics

* 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

* Changes Cupertino page transition curves to make paging animations more similar to those of native iOS

This reverts commit 71e9bd6f.

This is just a shorthand for
Scrollable.ensureVisible(tester.element(finder))

Fixes #8185

* Future<void> main

* Future<void>.delayed

* prefer_void_to_Null

* address review comments

* Refactor of cupertino/material/widgets app

* update docs 

* Update tests for const

This reverts commit 61cf946b.

* Make CupertinoApp and MaterialApp both use WidgetsApp for Navigator

* Make CupertinoApp and MaterialApp const constructors

* Make WidgetsApp routes aware

* Update tests

* enable lint unnecessary_new

* fix tests

* fix tests

* fix tests

* Fixes resulting from audit of issues links

I looked at every link to GitHub in our repo. For cases where we had a TODO that was waiting for a bug to be fixed, and the bug has now been fixed, I applied the pending change. For cases where the link was out of date, I updated the link.

* Update run_test.dart

skip this test again since it failed on linux and macos bots

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.

* Support all keyboard actions. (#11344)

The new matcher package deprecates isInstanceOf which seems eggregious.

Some APIs (such as the ones in package:test) assume you're running
in a child zone of the test zone by attempting to extract information
from the zone values. When we run runAsync() in the root zone, those
zone values are lost, and such API methods don't work.

The solution is to run in a child zone, but with a specification that
says to use the Root zone for task scheduling (both timers and
microtakss).

Follow-up to https://github.com/flutter/flutter/pull/17063

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

This will allow callers to run real async code within a widget test.

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

* Wrap `expectLater()` in flutter_tester so that callers can
  wait for the matcher to complete in their tests

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

* Add a way to generically go back on both Material and Cupertino scaffold pages

* review

* lint

* review

* Fix text assert text

Various improvements (in particular a new painting fuzzer) to the text manual test.

Some additional documentation.

A fix to Stack to remove an LTR bias: make unpositioned children apply "alignment".

Some more debugging information on RichText and Text.

A fix to the flutter tool to not crash when an RPC call throws an exception.