fix: expose extra dependencies transitively to library users

[chanseokoh]

This is about the "self-service" generated libraries.

We changed the dependency "scope" from the obsolete compile to implementation when we upgraded Gradle, which prevents affected dependencies from transitively exposed to library users. We did the same to gax a while ago and a report like this ensued there. Likewise, today I got a report where a library user cannot access auto-generated proto stub classes in their Java code.

This PR changes the scope back to what compile meant in old Gradle versions. The behavior after the change should be that of the old versions.

I've tracked down which dependencies are being affected and used in practice. I think the best course of action is to go back to the original behavior for safely, even though this could be over-provisioning.

[codecov]

Codecov Report

Merging #899 (a5a5d66) into main (7875565) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #899   +/-   ##
=======================================
  Coverage   87.84%   87.84%           
=======================================
  Files         153      153           
  Lines       15966    15966           
  Branches     1155     1155           
=======================================
  Hits        14025    14025           
  Misses       1601     1601           
  Partials      340      340           

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 7875565...a5a5d66. Read the comment docs.