Currently same as ms_ima_bytes_to_samples, but this will change; renamed
for consistency with all other IMA variations. Also clean a bit some
metas since I was testing anyway.
To support future MPEGs of uncertain layout and frame variations (namely
EALayer3) the code has been restructured: mpeg_decoder does stream
procesing and decoding, while mpeg_custom_utils_x does init and parsing
(write to data buffer + update offsets), per MPEG subtype. Internals
have changed but still gives byte-exact results.
AHX has been adapted to this format as a test. Some modes
(P3D/EALayer3/LyN/AWC) are defined for later development but will fail
on init ATM.
EA's MT/MicroTalk is not the early version of EAXA as I thought, but a
rarely used VBR codec (ex. FIFA 2001/2002 PS2) seemingly related to
Westwood VBR ADPCM
