Frame processing threading APIs

[natario1]

• New: setFrameProcessingPoolSize(): the number of Frames that can exist at any given moment
• New: setFrameProcessingExecutors(): the number of threads involved in Frame processing

The pool size should always be = number of executors + 1.

[codecov]

Codecov Report

Merging #716 into master will decrease coverage by 0.5%.
The diff coverage is 91.1%.

Impacted Files	Coverage Δ	Complexity Δ
.../otaliastudios/cameraview/engine/CameraEngine.java	82.1% <ø> (-8.2%)	29 <0> (-3)
...m/otaliastudios/cameraview/frame/FrameManager.java	89.4% <100%> (-6.1%)	16 <0> (ø)
...liastudios/cameraview/engine/action/LogAction.java	100% <100%> (ø)	5 <0> (ø)	⬇️
...liastudios/cameraview/engine/CameraBaseEngine.java	81.4% <100%> (+0.2%)	97 <5> (+3)	⬆️
...otaliastudios/cameraview/engine/Camera1Engine.java	71% <80%> (-0.7%)	53 <1> (ø)
...otaliastudios/cameraview/engine/Camera2Engine.java	73.7% <88.9%> (-0.1%)	105 <4> (ø)
.../java/com/otaliastudios/cameraview/CameraView.java	79.4% <90.5%> (+0.2%)	198 <5> (+5)	⬆️
...liastudios/cameraview/engine/meter/FocusReset.java	66.7% <0%> (-14.3%)	3% <0%> (ø)
...raview/engine/orchestrator/CameraOrchestrator.java	73.4% <0%> (-12.8%)	11% <0%> (-4%)
...studios/cameraview/engine/meter/ExposureReset.java	51.9% <0%> (-11.1%)	3% <0%> (ø)
... and 7 more