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
(cherry picked from https://android-review.googlesource.com/q/commit:ca6e67a66ba3448b00bd24762ab9494fb54fa8cd)
Merged-In: Ib2776dfc6c67b2042fb2f43a1251cd6f0ba61dc7
Change-Id: Ib2776dfc6c67b2042fb2f43a1251cd6f0ba61dc7