Add manual tag to proto_library at the root package

This is a fix similar to aosp/2707793. This adds manual tags to the
top-level proto_library created in the root package, plus any
dynamically created proto_library targets for proto.include_dirs. These
proto_library targets might not specify their deps correctly and might
be unbuildable.

(We need to keep these targets because they provide a ProtoInfo for
cc/java/py source gen)

Test: go test ./bp2build
Change-Id: Ic00f05186327fcfcc8d33a0a2c0891ed619b7acb