Move Flutter Gallery to dev/integration_tests/ as it is an older copy used only for testing. The current version of the Flutter Gallery now lives in https://github.com/flutter/gallery.

Reland of #52149

This reverts commit 357fd2db.

Revert "[flutter_tools] Allow providing dart-defines to Android, iOS, macOS builds (#51714)" (#52041)

This reverts commit ee60eeea.

This is required to roll forward package:vm_service to 3.0.0 and is
blocking a DevTools release.

The original commit actually *enabled* the test by removing the
flaky: true field in the commit.

This reverts commit 1d3fcfd6.

Now that the new schema is supported on the stable channel, and the old
schema is considered legacy, the template should always create plugins
using the new schema.

Fixes #51010

The test package differentiates between passing and not passing this
argument. A previous version had a bug that treated passing `0`
identically to not passing the argument, and the flutter test runner
relied on this bug by always passing a value and using a default of `0`.

- Remove the argument defaults throughout to make it clear that `null`
  is a valid value and the default.
- Remove the argument defaulting on the argument parser.
- Update the wording of the usage for this argument, this will also be
  updated on the `package:test` side.

This reverts commit e4fbb1ab.

This reverts commit d3387bc9.

* Fix stack trace parsing on non-debug builds; add e2e tests