Move annotations in public api to frameworks/base

These two are the only annotations in the android.annotations package
that are not @hide -- they are actually in the public API.

As such, they are not suitable in the annotations library. Move them
back to frameworks/base where the other core java APIs live.

Bug: 186197911
Test: m
Merged-In: Ide01e4e7840bddf1e024e9024771e528d17a1d80
Change-Id: Ide01e4e7840bddf1e024e9024771e528d17a1d80