Camera2: Fix broken onCaptureBufferLost callback

Turns out this never worked. 😱

- Add missing oncaptureBufferLost proxy method
- To avoid this issue in the future, change CameraDeviceImpl.CaptureCallback to be
  an interface instead of an abstract class; now all implementers _must_ implement
  all the methods
- For the short-circuit local callback when no callback is provided by the user,
  implement all no-ops explicitly.

Test: Camera CTS continues to pass; manual testing with injected buffer drops
Bug: 62004599
Change-Id: I7732903dbc00e80084162e067de66b5db6cee74c