ExifInterface: add support for reading metadata from RAW images

This CL depends on piex (github.com/google/piex),
which is owned by Google Photos's RAW team.

piex is capable of reading EXIF data that contains
metadata, and finding the positions in an image of
thumbnail and preview images from RAW images.

piex supports DNG, CR2, NEF, NRW, ARW, RW2, ORF
and RAF image file formats.

ExifInterface gets thumbnail and metadata information
from the above RAW image formats via piex.

Bug: 26177215
Change-Id: I529f8032bcb2a9d3d9e857ff1365a26a4f040066