Switch @IntDef from long to int, and add @LongDef

This CL mirrors changes made to the android.support.annotation version
of IntDef, to keep the usage and semantics identical (though the
internal version of @IntDef and @LongDef are of course hidden and not
part of the SDK.)

Test: These annotations have source retention and therefore have
no runtime impact; the change was compiling the SDK.

Change-Id: Idaf47e8d983c88be1bd8f938615c86611014b45a