Fix prebuilt mutator ordering in tests

Previously, the prebuilt mutators were added by the
cc.RegisterRequiredBuildComponentsForTest() function as a convenience
but unfortunately it lead to some of the mutators being in a different
order in the tests than in the normal build.

This change:
* Extracts the RegisterPrebuiltMutators() call from
  cc.RegisterRequiredBuildComponentsForTest()
* Makes sure that the prebuilt mutators are registered before the
  visibility gatherer and enforcer mutators.

Bug: 162505935
Test: m nothing
Change-Id: I7d959b558200b502f0a5e4653c41ea01414e142a
diff --git a/apex/apex_test.go b/apex/apex_test.go
index 0959a49..bfd7dfe 100644
--- a/apex/apex_test.go
+++ b/apex/apex_test.go
@@ -236,13 +236,15 @@
 	ctx.PreArchMutators(android.RegisterComponentsMutator)
 	ctx.PostDepsMutators(android.RegisterOverridePostDepsMutators)
 
-	cc.RegisterRequiredBuildComponentsForTest(ctx)
+	android.RegisterPrebuiltMutators(ctx)
 
-	// Register this after the prebuilt mutators have been registered (in
-	// cc.RegisterRequiredBuildComponentsForTest) to match what happens at runtime.
+	// Register these after the prebuilt mutators have been registered to match what
+	// happens at runtime.
 	ctx.PreArchMutators(android.RegisterVisibilityRuleGatherer)
 	ctx.PostDepsMutators(android.RegisterVisibilityRuleEnforcer)
 
+	cc.RegisterRequiredBuildComponentsForTest(ctx)
+
 	ctx.RegisterModuleType("cc_test", cc.TestFactory)
 	ctx.RegisterModuleType("vndk_prebuilt_shared", cc.VndkPrebuiltSharedFactory)
 	ctx.RegisterModuleType("vndk_libraries_txt", cc.VndkLibrariesTxtFactory)
@@ -5542,6 +5544,7 @@
 	ctx.RegisterModuleType("apex_key", ApexKeyFactory)
 	ctx.RegisterModuleType("filegroup", android.FileGroupFactory)
 	ctx.PreArchMutators(android.RegisterDefaultsPreArchMutators)
+	android.RegisterPrebuiltMutators(ctx)
 	cc.RegisterRequiredBuildComponentsForTest(ctx)
 	java.RegisterJavaBuildComponents(ctx)
 	java.RegisterSystemModulesBuildComponents(ctx)