This reverts commit 5fd259be.

Building an application for a desktop platform that transitively included any Dart-based plugins (such as path_provider) broke `flutter test`, because its compilation was overriding the provided main (in this case, the test main) with `generated_main.dart` if it was present. This PR:
- Changes the `flutter test` compilation path to update `generated_main.dart`, so that the tests will work, and will include any registered Dart plugins.
- Makes using `generated_main.dart` during recompile opt-in, to try to reduce the chance of a similar bug happening with other codepaths in the future.

Fixes https://github.com/flutter/flutter/issues/88794

[flutter_tools] read expression compilation results into memory before starting next compilation (#77867)

* opt out the flutter tool

* oops EOF

* fix import

* Update tool_backend.dart

* Update daemon_client.dart

* fix more

[flutter_tools] use initially parsed package config for language version, sound mode determination (#70323)

* [flutter_tools] null safety mode is used for dill naming

* add bad test case

If a file scheme and one or more roots is provided, fall back to this mapping before the direct file path if the file path cannot be turned into a package URI.

Use URI representation so that the transformation is resilient to the org-dartlang-app scheme used by the web builds.

Fixes #66095
Fixes #66404

This reverts commit af6ba867.

If a file scheme and one or more roots is provided, fall back to this mapping before the direct file path if the file path cannot be turned into a package URI.

Fixes #66095

complete removal of all generate functionality

Fixes #61508

Fixes additional bugs uncovered by tester, style fixes to prevent suggested imports.

Refactors KernelCompiler and ResidentCompiler to no longer use globals (except as a fallback for g3 migration). Improves the compilation error when running flutter test on a package without a flutter_test dependency.

Updates machine mode to output trace text to stderr

Also combines experiments into extraGenSnapshot/ExtraFrontEndOptions. Allows providing --no-sound-null-safety to allow out of order migration and running.

Support --enable-experiment in flutter test (for flutter_tester). Required minor change for null safety.