geom/m44750: occupancy context maps with on-the-fly update
Bitwise geometry occupancy coding uses a mapping table to select entropy contexts. This commit employs a dynamic mapping which is updated after each coding operation, replacing the previous static mapping tables. NB: the proposed version used a context with a halving period (max_count) of 64 symbols. However, this conflicts with another adoption (512 symbols), and a wholesale replacement of the arithmetic codec and context model. To resolve the conflict, the existing halving period (128) is used.