cameraserver: Output PIDs of all the client listeners in cameraservice dump

This allows better debugging data in dumpsys to note whether
certain clients (especially system processes) are registered as
listeners

Bug: 420864931

Test: camera dumpsys; see listener pids are correct

Flag: EXEMPT; bug fix
Change-Id: Ic0f68d6e4126c6a1eb529f43963e0bfbc3cb41ae