Lint to verify @SystemApi permissions; more docs.

Most @SystemApi methods should be protected with system (or higher)
permissions, so verify that system service methods are annotated with
any relevant @RequiresPermission.

Auto-document new @SystemService annotation to guide developers on
how to obtain manager instances.

Test: make -j32 update-api && make -j32 offline-sdk-docs
Bug: 62263906
Change-Id: I57ae661241557970af4328ff21abec7629492c7c
11 files changed