Move hiddenapi singleton rules to Soong

Move the rules that build hiddenapi-stubs-flags.txt,
hiddenapi-flags.csv and hiddenapi-greylist.csv into Soong.

Bug: 123645297
Test: m checkbuild
Test: m UNSAFE_DISABLE_HIDDEN_API_FLAGS=true
Change-Id: I90bf58710f6153ee8565994f799d3ec5699bc7fa
diff --git a/Android.bp b/Android.bp
index 591e5c8..92a6e9d 100644
--- a/Android.bp
+++ b/Android.bp
@@ -251,6 +251,7 @@
         "java/gen.go",
         "java/genrule.go",
         "java/hiddenapi.go",
+        "java/hiddenapi_singleton.go",
         "java/jacoco.go",
         "java/java.go",
         "java/jdeps.go",