Added sample code for using plugins and channels from background isolates

[gaaclarke]

Do not land until the feature is on stable.

fixes https://github.com/flutter/flutter/issues/112235

Pre-launch Checklist

• [x] I read the Flutter Style Guide recently, and have followed its advice.
• [x] I signed the CLA.
• [x] I read the Contributors Guide.
• [x] I updated/added relevant documentation (doc comments with ///).
• [x] All existing and new tests are passing.

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[gaaclarke]

@goderbauer please take a look.

[gaaclarke]

Thanks @goderbauer!

[domesticmouse]

@gaaclarke please merge latest from main to clean up CI results. Thanks!

[gaaclarke]

@gaaclarke please merge latest from main to clean up CI results. Thanks!

Done, FYI I'm waiting on the feature to land on stable to merge this. I'll add a note to the description and get it all set.

[domesticmouse]

@gaaclarke please merge latest from main to clean up CI results. Thanks!

Done, FYI I'm waiting on the feature to land on stable to merge this. I'll add a note to the description and get it all set.

Has this code been added to the list of CI targets in:

• https://github.com/flutter/samples/blob/main/tool/flutter_ci_script_stable.sh
• https://github.com/flutter/samples/blob/main/tool/flutter_ci_script_beta.sh
• https://github.com/flutter/samples/blob/main/tool/flutter_ci_script_master.sh

[domesticmouse]

Hey @gaaclarke, I'm wondering if this feature is in beta. If yes, I'll be rolling a beta uber PR that will land when stable increments that this PR could be included in.

[gaaclarke]

@domesticmouse, yep! It's on beta.

[domesticmouse]

Integrated into https://github.com/flutter/samples/pull/1556

[domesticmouse]

This should now be closeable. To be sure, please resolve conflicts and you should hopefully see this PR resolve to 0 files changed.

[domesticmouse]

Land once CI turns green.