Ready more build rules for dir move

Tweak some visibilities and set up more filegroups to enable moving
the ApiDocs.bp and StubLibraries.bp files into the api subdir.

Bug: 271563074
Test: m
Change-Id: Ib2776dfc6c67b2042fb2f43a1251cd6f0ba61dc7

core/java/Android.bp

@@ -429,6 +429,11 @@ aidl_interface {
     },
 }
 
+filegroup {
+    name: "frameworks-base-java-overview",
+    srcs: ["overview.html"],
+}
+
 // Avoid including Parcelable classes as we don't want to have two copies of
 // Parcelable cross the libraries. This is used by telephony-common (frameworks/opt/telephony)
 // and TeleService app (packages/services/Telephony).