Support testing for resource shrinking

Add a simple test and add necessary mock dependencies to allow future
resoure shrinking use with platform targets.

Test: m
Bug: 202959019
Change-Id: Id2dd44d52ce5ea62c06784caab0af6276248cb3f

java/testing.go

@@ -74,6 +74,7 @@ var prepareForTestWithFrameworkDeps = android.GroupFixturePreparers(
 		// Needed for R8 rules on apps
 		"build/make/core/proguard.flags":             nil,
 		"build/make/core/proguard_basic_keeps.flags": nil,
+		"prebuilts/cmdline-tools/shrinker.xml":       nil,
 	}.AddToFixture(),
 )