Let 'r' uart monitor command show details of current megabyte selection used by MAP

[gurcei]

Is your feature request related to a problem? Please describe.
Presently, the uart monitor's "r" command only emits MAPL and MAPH details pertaining to the current map state, which provides details of what 8kb chunks of the current megabyte selection have been mapped into the 16-bit address space. But no mention is made of what is the currently selected megabyte.

Describe the solution you'd like
Two more fields added into the 'r' command's output, let's say:

• "MH" (for bits 20-27 describing megabyte selected for MAPH)
• "ML" (for bits 20-27 describing megabyte selected for MAPL)

E.g.:

                                                                                       \/ \/
PC   A  X  Y  Z  B  SP   MAPH MAPL LAST-OP In     P  P-FLAGS   RGP uS IO ws h RECA8LHC MH ML
E1B2 00 01 18 00 00 01F0 B300 E300 F0FA    00     22 ..E...Z. ...P 18 -  00 - ..c..lhc 00 00

Describe alternatives you've considered
I'm aware that I could also retrieve such information via the hyppo_get_mapping hyppo call, but I feel when we need this information during a debugging session over the uart monitor with the cpu paused (e.g., via m65dbg), trying to make hyppo calls in that situation is quite awkward (though not impossible, m65dbg already does tricks like this). So I feel a more ideal solution would be to add such fields into the existing 'r' register command.