Move hidden API metadata file rule to platform_bootclasspath

This change moves the monolithic hidden API index file creation rule
from the hiddenAPISingleton into the platform_bootclasspath.

Bug: 179354495
Test: verified that the out/soong/hiddenapi/... files are unchanged
      by this change
Change-Id: Ib25be3618e30a83dc2929a18062eb58eefdabefb
diff --git a/java/platform_bootclasspath_test.go b/java/platform_bootclasspath_test.go
index 9e0235b..417c6bf 100644
--- a/java/platform_bootclasspath_test.go
+++ b/java/platform_bootclasspath_test.go
@@ -173,7 +173,7 @@
 	android.AssertStringEquals(t, "platform dist goals call", "$(call dist-for-goals,droidcore,out/soong/hiddenapi/hiddenapi-flags.csv:hiddenapi-flags.csv)\n", android.StringRelativeToTop(result.Config, goals[1]))
 }
 
-func TestPlatformBootclasspath_HiddenAPIMonolithicIndexFile(t *testing.T) {
+func TestPlatformBootclasspath_HiddenAPIMonolithicFiles(t *testing.T) {
 	result := android.GroupFixturePreparers(
 		hiddenApiFixtureFactory,
 		PrepareForTestWithJavaSdkLibraryFiles,