Rename the ojluni-annotated-stubs target.

All of the annotations under this are intended for use in the SDK. In
order to make this clear (because other types of annotations are
planned), this change renames the target to
ojluni-annotated-sdk-stubs.

Bug: 115746226
Test: `make api-stubs-docs`
Change-Id: I11366b6293b681cb4c8118fc117601a671c33282