Bazel: Improve protobuf rule detection
Bazel: Improve protobuf rule detection

Improve the regex to also detect protobuf rules in plugins. Also fix the
source library extraction from the protobuf rules.

Bug: Issue 11670
Change-Id: I9a18ae230919c6fa0a9b6685943949c4f9af9c32

GerritCodeReview/gerrit,GerritCodeReview/gerrit,GerritCodeReview/gerrit,GerritCodeReview/gerrit,GerritCodeReview/gerrit,GerritCodeReview/gerrit,GerritCodeReview/gerrit,GerritCodeReview/gerrit