Reland: Allow resetting test invariants in addTearDown - #193476

Flutter's recent change
flutter/flutter#193476
moved the test harness's check for pending frame callbacks. It now
runs after the test's `addTearDown` callbacks, instead of right after
the harness's final pump.

Loading a font sends a `fontsChange` message, and text in the tree
reacts by scheduling a frame callback. When a `testWidgets` body loads
a font, the message is handled only after the final pump, so the
callback never runs. The check used to miss such callbacks, but now it
finds them. As a result, 178 tests in emoji_reaction_test and
katex_test failed with "An animation is still running even after the
widget tree was disposed".

Loading the fonts in `setUpAll` avoids this, because that runs before
any test has put text in the tree. Fonts persist across tests anyway.

Co-Authored-By: Claude Sonnet 5.5 <[email protected]>
Co-Authored-By: Claude Opus 5.5 <[email protected]>

)

This PR relands flutter#192082 after fixing the error in integration tests as
described in flutter#193383.

I've manually verified that the integration test fails on flutter#192082 and
passes now.

### Why it failed

This integration test runs
`dev/automated_tests/flutter_test/ticker_test.dart`, which leaves a
`Ticker` running. It expects that test to fail with an "An animation is
still running even after the widget tree was disposed." error. After
flutter#192082, `ticker_test.dart` passed instead.

The leaked ticker is caught by
`SchedulerBinding.debugAssertNoTransientCallbacks`. Unlike most
invariant checks, it doesn't throw; it reports the failure through
`FlutterError.reportError`. During a test, `FlutterError.onError` stores
reported errors in `_pendingExceptionDetails`, and the test completion
handler reports them when `runTest` finishes. Changing the behavior of
this method would be a breaking change to the public API in the
framework, so instead the test framework should be changed to pick up
this error.

Before flutter#192082, the check ran inside `_runTestBody`, so the completion
handler picked up the error. flutter#192082 moved the check to `postTest`,
which runs after the completion handler. The `try/catch` in `postTest`
only catches thrown errors, and `postTest` then clears
`_pendingExceptionDetails`, so the error was silently dropped and the
test passed.

#### What this reland changes

See the [2nd
commit](flutter@c617498)
for the list of changes.

- After running the invariant checks, `postTest` also picks up
`_pendingExceptionDetails` and reports it. If a check also threw, the
thrown error is reported and the other one is printed to the console so
it isn't lost.
- `postTest` now passes the test description to `reportTestException`
instead of `''`, so the output includes `The test description was: ...`
again. The integration test's expected output relies on that line.
- The four `_verify*Unset` helpers go back to
`FlutterError.reportError`, which is what they used before flutter#192082. Now
that `postTest` handles reported errors, they don't need to throw, and
they behave the same as before. flutter#192082 made this change with the hope
to simplify and unify the code flow, but now that we have to pick up
`_pendingExceptionDetails` anyway, there's no reason to make this
change.

#### Tests

- Added a test to `bindings_invariants_test.dart`. It leaks a `Ticker`
and checks that `postTest` reports the error along with the test
description.
- `test_test.dart: flutter test should report a nice error when a Ticker
is left running` passes again.

### What the 3rd commit changes

The [3rd
commit](flutter@6866134)
refactors the `bindings_invariants_test.dart` to ensure that the
`postTest` is run (and invariants are reset) even when errors occur
during the test body.

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linked a website documentation issue or PR in [flutter/website] (or
verified none is needed).
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[test-exempt].
- [ ] I followed the [breaking change policy] and added [Data Driven
Fixes] where supported.
- [ ] All existing and new tests are passing.

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* test: the tests pass on Flutter 3.50

Load the fonts in setUpAll instead of in a testWidgets body. A font loaded in the body sends its fontsChange message after the test has ended, and since Flutter 3.50 (flutter/flutter#193476) the transient callback check runs after it arrives. loadImpaktfullUiFonts now throws when it is called inside a testWidgets body.

* build: the example app builds for Android on Flutter 3.50

Flutter 3.50 needs Gradle 9.3.1 or newer; the example was on 9.1.0.

* feat: impaktfull_ui is built on material_ui and cupertino_ui for Flutter 3.50

Flutter 3.50 deprecates package:flutter/material.dart and
package:flutter/cupertino.dart: Material and Cupertino moved into the
packages material_ui and cupertino_ui. Every import of the package, its
tests, the example app and the code templates of tool/cli now use them
(the change of dart fix --code=migrate_design_widgets, applied as a plain
import swap so no file is reformatted), and flutter analyze is clean
again on Flutter 3.50.

impaktfull_ui needs Flutter 3.47 or newer, the minimum of material_ui.
The Dart SDK constraint stays where it was, so the language version and
with it the formatting of the code do not change in this release.

material_ui is a separate copy of Material, so a ThemeData passed to
ImpaktfullUiApp comes from material_ui now. ImpaktfullUiApp puts
MaterialUiCompatibilityBridge around its pages, so pages and packages that
still use package:flutter/material.dart keep their theme and their
material localizations while they migrate. The README explains the
migration of an app.

The golden helpers give the material_ui theme the obscured font of the
alchemist theme, because alchemist 0.14 still builds its golden app with
package:flutter/material.dart; without it every CI golden changed.
test_fixes imports TabController from material_ui, the import dart fix
now migrates.

* build: the example app uses Android Gradle Plugin 9.1.1, the minimum of Flutter 3.50