[non-BE] Resolve "Incorrect metadata read index in OMASA LS and SH rendering"
Related to #687 (closed). Uses md_idx
for fetching metadata in OMASA LS and SH rendering, as it is updated correctly for each subframe, unlike the previously used dirac_read_idx. As a result, the metadata is updated for each subframe in rendering, instead of only once in a frame.
This is non-BE for OMASA rendering to LS and Ambisonics.
Review from @bayers is most logical.