Refactor cc/sabi.go

* Rename `vndk_deps` mutator to `sabi_deps` to better reflect its
  purpose.
* Eliminate duplication of ABI dump generation logic. sabiDepsMutator
  should call libraryDecorator.shouldCreateSourceAbiDump() to determine
  if a module needs to be marked with CreateSAbiDumps.
* Non-VNDK libraries that are opt-in to ABI check would have their
  dependencies correctly marked with CreateSAbiDumps.
* Refactor some lines to idiomatic syntax.
* Add comment strings.

Bug: 145608479
Bug: 173492236
Test: TH presubmit
Change-Id: I99e97787bdf2a4f0c970809161b64aa668ff3d1a