SystemApi is parameterized

We have decided to reuse the existing annotation @SystemApi for all Java
APIs regardless of whether they are for apps or platform internal
modules. This was because introducing new annotation types every time
when we have to create new API surfaces will only increase the confusion
without giving much benefit.

Instead, to differenciate the different API surfaces of @SystemApi, the
annotation type is parameterized. Specifically, it has to axises.

client: specifies the intended client of the API.

process: specifies the process(es) that the API is available.

The default for client and process are priv-apps and all, respectively,
which corresponds to the today's @SystemApi for privileged apps like
GMS.

Bug: 140202860
Test: m
Change-Id: I3305b71e22970e80db95f3daf3d7713603c7d68d