camera2: (LEGACY) Add face detection support and vstab modes

Also work-around CTS freezing forever in Camera#setPreviewTexture

* Set preview texture to null after unconfiguring (Camera#stopPreview)
* Remove all uses of recording hint

(Some devices disable face detection unconditionally when recording is not
using HDR mode; recording hints will be introduced after we add
capture intent support)

Change-Id: I2f0a80f1d580af214cb0f53abcbf33c7391790f1