Add genrule to build *.latest.version build target.

Build a new target *.latest.version which will contain a text file
containing the last finalized version.

Bug: 242316893, 282140551
Test: atest prebuilt_apis_test
(cherry picked from https://android-review.googlesource.com/q/commit:daa314ac97d5ab8076113ee7f269b4e4cc3cf620)
Merged-In: I41fa91c9ec273f342b7807c66c4d65ba13260124
Change-Id: I41fa91c9ec273f342b7807c66c4d65ba13260124