* Standardize on .g.dart
* Remove unused exclusion patterns
* Mark pigeons/ as dev-only in the tooling
* Version bumps
* Add missed files
* More new import fixes
Pigeon has an usual test structure since it generates test code to run
in a dummy plugin; add that structure to the list of recognized tests so
that changes to its platform tests won't be flagged by `version-check`.
Improves the logic used to determine whether to require a version and/or CHANGELOG change:
- Removes the requirement that dev-only (e.g., test) changes update the CHANGELOG, since in practice we were essentially always overriding in that case.
- Adds file-level analysis of `build.gradle` files to determine whether they are only changing test dependencies.
- Improves the "is this a published example file" logic to better match pub.dev's logic, to fix some false positives and false negatives (e.g., `rfw`'s `example/<foo>/lib/main.dart` being considered published).
Removes the no-longer-necessary special-case handling of some Dependabot PRs, as well as the PR-description-based system it was built on (and that turned out not to be very useful due to the way `CIRRUS_CHANGE_MESSAGE` actually worked). `build.gradle` analysis should not cover all such cases, and without the need to hard-code them by package name.
