Allow defining neverallow in packages other than android.

This exposes test func on ValueMatcher and helpers relevant for testing neverallows.

Bug: 153333044
Test: m
Change-Id: Ied07cd33afa537f9d7aa3c33e59f4ac985901a0f
diff --git a/android/neverallow_test.go b/android/neverallow_test.go
index 0373b79..2fc42e3 100644
--- a/android/neverallow_test.go
+++ b/android/neverallow_test.go
@@ -313,7 +313,7 @@
 		t.Run(test.name, func(t *testing.T) {
 			// If the test has its own rules then use them instead of the default ones.
 			if test.rules != nil {
-				setTestNeverallowRules(config, test.rules)
+				SetTestNeverallowRules(config, test.rules)
 			}
 			_, errs := testNeverallow(config)
 			CheckErrorsAgainstExpectations(t, errs, test.expectedErrors)
@@ -327,7 +327,7 @@
 	ctx.RegisterModuleType("java_library", newMockJavaLibraryModule)
 	ctx.RegisterModuleType("java_library_host", newMockJavaLibraryModule)
 	ctx.RegisterModuleType("java_device_for_host", newMockJavaLibraryModule)
-	ctx.PostDepsMutators(registerNeverallowMutator)
+	ctx.PostDepsMutators(RegisterNeverallowMutator)
 	ctx.Register(config)
 
 	_, errs := ctx.ParseBlueprintsFiles("Android.bp")