There were four or five different implementations in various tests for sendFakeKeyEvent, which roughly all did the same thing. I was going to add yet another one, and decided that it needed to be generalized and centralized. This replaces those instances with something that just takes a LogicalKeyboardKey so that it's self-documenting, and can be used with multiple platforms.

This adds two functions to widget tester: sendKeyDownEvent and sendKeyUpEvent which simulate key up/down from a physical keyboard. It also adds global functions simulateKeyDownEvent and simulateKeyUpEvent that can be called without a widget tester. All are async functions protected by the async guard.

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

In order not to break existing benchmarks.

* Add semanticsEnabled to widgetBenchmark
* Add button_matrix_app and gesture benchmark

# Description
Currently the benchmarks test prints a scary warning message, even when it passes, that a benchmark is being run with asserts enabled.

Normally we don't want developers to do this, because the performance of code with asserts is not characteristic of what end-users will experience. However, we need to unit-test benchmarkWidgets, so I've added a contraindicated option to suppress the warning for the test.

# Related Issues
25049 (comment)

This also fixes up some indentation in some
bulleted lists.

https://github.com/dart-lang/dartdoc/issues/1969

* Make it easier to ensure semantics

* fix indentof statements in BlockFunctionBody

* fix indentof statements in BlockFunctionBody in tests

* 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

* Add docs and sample for takeException

* fix sample

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

* prefer_void_to_null in flutter_test

* fix CI

* enable lint unnecessary_new

* fix tests

* fix tests

* fix tests

The verbosity change is to help track down timeouts that currently look like:

```
C:\Windows\Temp\flutter sdk>call bin\flutter.bat config --no-analytics
Checking Dart SDK version...
Downloading Dart SDK from Flutter engine c5a63d28bf3735569c8187753bc490d8351a8363...
Unzipping Dart SDK...
Updating flutter tool...
```

The new matcher package deprecates isInstanceOf which seems eggregious.

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)

This should reduce the number of flakes without actually increasing
the timeout, so we'll still find out quickly if a test is hanging.

The numbers here might need tweaking. Maybe the default two seconds is
too short for CI bots.