The build takes ~2 hours when there are changes to core modules that
force re-running of all tests.
Ran into the long test times (again) in #7632.
This also affects release times since the version bump PR build takes 2
hours to run, and then another 2 hours to run release (or wait 2 hours
for CI build to run and update gradle cache).
* Sync gradle-plugins version with main project
* More fixes
* Can rely on examples build against all branches now?
* Use common version.gradle.kts
* Update doc
* Simplify
* Include gradle-plugins as a composite build
* Make gradle-plugins project independent from the main one
* Delete old ClassRef and friends
* Fixes
* Polish
* Polish
* Simplify
Trask Stalnaker