Camera: Camera shouldn't throw 'RejectedExecutionException'

In case the camera client registers a valid callback but the
respective handler looper exits a 'RejectedExecutionException'
could be thrown by the 'HandlerExecutor' implementation once it
detects that the 'post' method is failing. This exception is not
mentioned in the current camera API and deviates from the usual
behavior where the post status is ignored. To avoid possible
issues with camera clients a new camera specific handler executor
is used which will also ignore the 'post' method return value.

Bug: 74605221
Test: Camera CTS
Change-Id: I2d947ba9cebfc9b4b2a7c88ace6a4060ff7c175e