* Added sample code for using plugins and channels from background isolates.
* goderbauer feedback 1
* goderbauer feedback2
* goderbauer feedback 3
* Add `background_isolate_channels` to CI
* Comment in `background_isolate_channels`
* Fixup
* Elide `experimental/material_3_demo` from `master`
* Elide `material_3_demo` from `master` CI
* Elide `place_tracker` on `master` CI
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Co-authored-by: Brett Morgan <brettmorgan@google.com>
Co-authored-by: Brett Morgan <brett.morgan@gmail.com>
