Android libcamera_metadata

This is a copy of the libcamera_medatada from Android goog/pi-arc-dev branch:

• Copy include/ and src/*.c from android/system/media/camera/
• Copy include/camera_metadata_hidden.h from android/system/media/private/camera/include/
• Modify camera_metadata.c to fix compile errors. The diffs can be found in src/diff/