Enable annotations for framework stubs

Keeps Nullable and other source retention annotations in the stubs.

Bug: 157010342
Test: diff_stubs.sh
Change-Id: I4fc66d607276ff885947489afd63e1370ec85939
Merged-In: I4fc66d607276ff885947489afd63e1370ec85939
(cherry picked from commit 01ff6b243febc199ffe718a49374af954c6dbeff)
1 file changed