Export monolithic hidden API files from platform_bootclasspath

Makes the monolithic hidden API files accessible from the
platform_bootclasspath so they can be output to the dist build target
and used by other modules, e.g. by doing something like this:
  java_resources: [
    ":platform-bootclasspath{hiddenapi-flags.csv}",
  ],

It makes the paths relative to the out/soong/hiddenapi directory rather
than the out/soong directory to make them easier to use in the
java_resources property without changing the structure of the APK.
Without that attempting to use them in a java_resources property will
result in them being copied to a hiddenapi/ within the APK instead of
being used at the top level as existing APKs like
CtsHiddenApiBlocklistTestApiTestCases expect.

Bug: 177892522
Test: m nothing
Change-Id: I829412fc7d25411e0c2e0713d0d219a18f4af2ee
diff --git a/java/hiddenapi_singleton.go b/java/hiddenapi_singleton.go
index 641e19f..37c394a 100644
--- a/java/hiddenapi_singleton.go
+++ b/java/hiddenapi_singleton.go
@@ -101,11 +101,15 @@
 // yet been created.
 func hiddenAPISingletonPaths(ctx android.PathContext) hiddenAPISingletonPathsStruct {
 	return ctx.Config().Once(hiddenAPISingletonPathsKey, func() interface{} {
+		// Make the paths relative to the out/soong/hiddenapi directory instead of to the out/soong/
+		// directory. This ensures that if they are used as java_resources they do not end up in a
+		// hiddenapi directory in the resulting APK.
+		hiddenapiDir := android.PathForOutput(ctx, "hiddenapi")
 		return hiddenAPISingletonPathsStruct{
-			flags:     android.PathForOutput(ctx, "hiddenapi", "hiddenapi-flags.csv"),
-			index:     android.PathForOutput(ctx, "hiddenapi", "hiddenapi-index.csv"),
-			metadata:  android.PathForOutput(ctx, "hiddenapi", "hiddenapi-unsupported.csv"),
-			stubFlags: android.PathForOutput(ctx, "hiddenapi", "hiddenapi-stub-flags.txt"),
+			flags:     hiddenapiDir.Join(ctx, "hiddenapi-flags.csv"),
+			index:     hiddenapiDir.Join(ctx, "hiddenapi-index.csv"),
+			metadata:  hiddenapiDir.Join(ctx, "hiddenapi-unsupported.csv"),
+			stubFlags: hiddenapiDir.Join(ctx, "hiddenapi-stub-flags.txt"),
 		}
 	}).(hiddenAPISingletonPathsStruct)
 }