Refactor mixed build allowlist handling

This refactoring prepares for introduction of bazel prod mode, an
alternative mechanism for mixed builds allowlist handling.

 * Decide bazel-mode as close to soong_build main as possible
 * BazelContext itself decides whether a module is allowlisted
 * Separate bp2build and mixed build allowlist

Test: m nothing, manually verified all modules are mixed build disabled
(via metrics)
Test: USE_BAZEL_ANALYSIS=1 m nothing, manually verified that mixed build
disabled/enabled modules are identical before and after change.

Change-Id: I0f55d8b85000cb4a871a099edc6d7d868d7df509

cc/library.go

@@ -282,7 +282,7 @@ func libraryBp2Build(ctx android.TopDownMutatorContext, m *Module) {
 	// For some cc_library modules, their static variants are ready to be
 	// converted, but not their shared variants. For these modules, delegate to
 	// the cc_library_static bp2build converter temporarily instead.
-	if android.GenerateCcLibraryStaticOnly(ctx.Module().Name()) {
+	if android.GetBp2BuildAllowList().GenerateCcLibraryStaticOnly(ctx.Module().Name()) {
 		sharedOrStaticLibraryBp2Build(ctx, m, true)
 		return
 	}