Add services-stubs for in-process APIs in services.jar

services-stubs is a stubs library for services.jar. It provides the
in-process APIs that's available inside the system server process
running services.jar.

Currently, all APIs in the jar are hidden by annotating
com.android.server package with @android.annotation.Hide. To add some
APIs,

1) remove package-info.java for com.android.server
2) add package-info.java for other sub packages
3) annotate them with @android.annotation.Hide except for the package
where the newly added APIs are in

This change also added android.annotation.Hide class which can be used
to hide an API without using the @hide javadoc tag. This opens up the
possibility of running metalava over the compiled jar, which is expected
to be much faster than when ran with source files.

Bug: 139391334
Test: m
Test: m services-stubs
Change-Id: I027b8a22b3e7533f6203aabb9dc3f690e4e842a6