Description

To make it clear which features are still experimental, these should be disabled for users on "stable" branches.

Related Issues

Fixes #30152

Tests

I added the following tests:

• flutter_command_test.dart: Experimental command can be disabled on stable branch.
• flutter_command_test.dart: Experimental command Works normally on regular branches

These verify that executing an experimental command on a stable branch throws a tool exit.

Checklist

Before you create this PR confirm that it meets all requirements listed below by checking the relevant checkboxes ([x]). This will ensure a smooth and quick review process.

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I signed the CLA.
• I read and followed the Flutter Style Guide, including Features we expect every widget to implement.
• I updated/added relevant documentation (doc comments with ///).
• All existing and new tests are passing.
• The analyzer (flutter analyze --flutter-repo) does not report any problems on my PR.
• I am willing to follow-up on review comments in a timely manner.

Breaking Change

Does your PR require Flutter developers to manually update their apps to accommodate your change?

• Yes, this is a breaking change (Please read Handling breaking changes). Replace this with a link to the e-mail where you asked for input on this proposed change.
• No, this is not a breaking change.