EmulatedCamera2: Improve thread sequencing

- When the readout thread is the slow point, frames could be dropped
  in various ways. Add signals to slow down the configure thread and
  the sensor when the readout thread is behind.

- Clean up verbose logs to be clearer

Bug: 6243944

Change-Id: I2efb909f03183273a71dc7edede3aa107117f558
4 files changed