relocates the static functions from metadata.h and adds MetadataCopy() to the interface Change-Id: I28bfa9233d3dd70dddf6b561fe0bf4be378db1ec
unused currently, but the intent is to allow each format to populate exif/xmp/icc with cwebp then transferring it to the webp file. Change-Id: I0514f62de52fa7f89c595ee7ef2ad7dced910a41