Add docs for setTargetSize and setTargetSampleSize

Bug: 77507530
Test: No change in behavior, no new tests

Add @Px and @IntRange annotations, and be explicit that setTargetSize
refers to pixels. Add a comment to setTargetSampleSize that is like
calling setTargetSize with particular values, to try to make it clear
how the two are related.

Change-Id: Ie7e9429bc8c548f44d382358c161425f666ba82f