libgui: add sampling fns to SurfaceComposerClient

{add,remove}RegionSamplingListener was missing from
SurfaceComposerClient. Add them here to make the JNI
connection easier.

Test: boot
Test: atest CompositionSamplingListenerTest
Bug: 124305231
Change-Id: Ifd8833c25c112743524cee0ac5f2eae035011161
2 files changed