Add update-api for Metalava based api-stubs-docs

Use check_api section to put the target files which need to be updated.
But check_api doesn't do actually checking work.

Bug: b/112668343
Test: m -j api-stubs-docs-update-current-api
Change-Id: I0f28e6e480413e0ac5cdff51bc4b2df478a867f6