Migrate all offline/online sdk docs generation to use Metalava

These targets all depend on libcore sources which are blocker for us to
enable java9 feature, so convert them to Metalava.

Also enable API level annotations for api-stubs-docs, offline-sdk-docs,
and online-sdk-docs.

Test: m -j docs
Bug: b/78245848
Change-Id: I354d699a79cc5e6580b50e0613e7602c77b9c0b5