Convert hiddenapi tests to use test fixtures

These tests rely on files provided by javaMockFS() so have been
converted to test fixtures to allow them to remove that dependency
which will allow javaMockFS() to be removed.

Bug: 182638834
Test: m nothing
Change-Id: Ifd4069a74fcf67e555f998ddbc4de3fde26b2aae

java/hiddenapi_singleton.go

@@ -31,6 +31,8 @@ func RegisterHiddenApiSingletonComponents(ctx android.RegistrationContext) {
 	ctx.RegisterModuleType("hiddenapi_flags", hiddenAPIFlagsFactory)
 }
 
+var PrepareForTestWithHiddenApiBuildComponents = android.FixtureRegisterWithContext(RegisterHiddenApiSingletonComponents)
+
 type hiddenAPISingletonPathsStruct struct {
 	// The path to the CSV file that contains the flags that will be encoded into the dex boot jars.
 	//