Converting GN's absl_source_sets to filegroups causes them to be
recompiled in every module that depends on them, 424 times for
absl/strings. Convert them to cc_library_static instead so they
only have to be compiled once per variant. This reduces the size
of the intermediates directory for external/webrtc from 26GB to 3.6GB.
Also remove the dependencies from cc_library_static modules, they
don't do anything and just increase the complexity in Soong's module
graph. All the transitive dependencies are already collected into the
final libwebrtc and webrtc_audio_processing modules.
Bug: 293194014
Test: m libwebrtc
Change-Id: Iebbafa52fa72364a70f4f35656af17a63c88b860
3ebcf712c8