Write annotations to project metadata, and provide them to pkl-doc\
The following annotations have meaning for pkl-doc:
* `@Unlisted`: hide package from documentation site
* `@Deprecated`: add deprecated information
- Fix and clean up the pkl-commons-test build script.
- Change tests to read test packages/certs directly from
the file system instead of packaging and reading them
from the class path.
- Update expected checksums of some test packages.
- Fix a conflict between Pkl's and Gradle's
Kotlin libraries in the pkl-gradle project.
- Fix build deprecation warnings.
- Ensure Gradle distribution integrity with `distributionSha256Sum`.
- Manually verify integrity of Gradle wrapper added by this commit.
