Add a public measurement-key remapping protocol so callers can safely rename result keys on individual…

Add a public measurement-key remapping protocol so callers can safely rename result keys on individual…: a task in MiMo-V2.6-RL-harbor-code: MiMo-V2.6-RL Code (Harbor) (Harbor dataset). Expose cirq.with measurement key mapping(val, key map, default=...) from the top-level package. It must dispatch…