Add update_makefile and change api file name

The update_makefile is added for automatically updating app_dirs. And
api file names are changed to api-stubs-docs_api.txt and
system-api-stubs-docs_api.txt, because droiddoc.go file was updated.

Test: ./update_prebuilts.py -f 99 4883641
Bug: 77577799
Change-Id: Ida02031c6412a6a2d39ea9652ece1f5650edf3b2
1 file changed