[truetype] Binary search through the `hdmx` records.
The `hdmx` table is supposed to be sorted by ppem size, which enables binary search. We also drop the check for the sufficient length of the record because it is now enforced when the table is loaded. * include/freetype/internal/tttypes.h (TT_FaceRec): Store the `hdmx` record pointers sorted by ppem instead of ppem's themselves. * src/truetype/ttpload.c (tt_face_load_hdmx): Prudently sort records. (tt_face_get_device_metrics): Implement binary search to retrieve advances.