* YJIT: Local variable register allocation

* locals are not stack temps

* Rename RegTemps to RegMappings

* Rename RegMapping to RegOpnd

* Rename local_size to num_locals

* s/stack value/operand/

* Rename spill_temps() to spill_regs()

* Clarify when num_locals becomes None

* Mention that InsnOut uses different registers

* Rename get_reg_mapping to get_reg_opnd

* Resurrect --yjit-temp-regs capability

* Use MAX_CTX_TEMPS and MAX_CTX_LOCALS