Android libcamera_metadata

Warning: This document is old & has moved. Please update any links:
https://chromium.googlesource.com/chromiumos/platform2/+/HEAD/camera/android/libcamera_metadata/README.md

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/