What type of PR is this?
Feature

What package or component does this PR mostly affect?
language/go

What does this PR do? Why is it needed?
This changes the gazelle's go_proto_library generation behavior.
Previously, in .proto file mode, gazelle would generate a separate go_proto_library target for each proto_library target, and these would have the same values for the importpath attribute. This caused build errors in certain situations.

This change makes Gazelle group proto_library targets which would otherwise have the same go_proto_library importpath, into a single go_proto_library using the protos attribute.

Which issues(s) does this PR fix?

Fixes #1724

Other notes for review

• While testing this PR, I ran bazelisk test //... and saw two tests fail

FAIL: //cmd/gazelle:gazelle_test (see /private/var/tmp/_bazel/7faad61fac7f6d421e59e31d0146c79e/execroot/_main/bazel-out/darwin_arm64-fastbuild/testlogs/cmd/gazelle/gazelle_test/test.log)
INFO: From Testing //cmd/gazelle:gazelle_test:
==================== Test output for //cmd/gazelle:gazelle_test:
could not locate go tool
================================================================================
FAIL: //internal:bazel_test (see /private/var/tmp/_bazel/7faad61fac7f6d421e59e31d0146c79e/execroot/_main/bazel-out/darwin_arm64-fastbuild/testlogs/internal/bazel_test/test.log)
INFO: From Testing //internal:bazel_test:
==================== Test output for //internal:bazel_test:
error: unknown runfile: ./.bazelrc
================================================================================

This looks like an environment issue. Looks like CI is green though, so I think we can ignore this.

• When generating a single go_proto_library target for multiple proto_library targets, the change creates a combinedImports platformStringsBuilder variable. I'm not sure if my general approach to combining the dependencies is correct, and would appreciate guidance.