Add bp2build support for cc_library_static.

Also refactor bp2build-related code for cc_library_headers.

(Retry of previous CL after the presubmit failed to detect a merge conflict)

Test: Added unit test.

Test: bp2build-sync.py write; bazel build //bionic/... still works (but bp2build is disabled for most cc_library_static targets for other reasons)
Change-Id: I2f4405c2fea305623bbc6daaaf62808b0c074216