Surface Java APIs Used By APK-only Modules.

Previously we were only generating used-by API-coverage for APEX modules.
This change adds support for APK-only modules such as NetworkStack and DocumentsUI.

Bug: b/216313756
Forrest Run: https://android-build.googleplex.com/builds/abtd/run/L10800000953846781

Test: TARGET_BUILD_VARIANT=userdebug PRODUCT=mainline_modules_x86 ./vendor/google/build/build_unbundled_coverage_mainline_module.sh -j16

Change-Id: Id17e4a55c2a52e9903632a654e778f8d54982dfc
Merged-In: Id17e4a55c2a52e9903632a654e778f8d54982dfc
(cherry picked from commit 56d75785bd)

apex/testing.go

@@ -24,7 +24,6 @@ var PrepareForTestWithApexBuildComponents = android.GroupFixturePreparers(
 	android.MockFS{
 		// Needed by apex.
 		"system/core/rootdir/etc/public.libraries.android.txt": nil,
-		"build/soong/scripts/gen_java_usedby_apex.sh":          nil,
 		"build/soong/scripts/gen_ndk_backedby_apex.sh":         nil,
 		// Needed by prebuilt_apex.
 		"build/soong/scripts/unpack-prebuilt-apex.sh": nil,