Medical - Add API for fully healing a unit

[DartRuffian]

When merged this pull request will:

• Add a public API function to full heal a unit
  • This is just a wrapper with some param checking
• Add optional parameter to medical_treatment_fnc_fullHeal to not add the full heal log message

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• Title of this PR uses our standard template Component - Add|Fix|Improve|Change|Make|Remove {changes}.

[DartRuffian]

Thought about adding a boolean flag to medical_treatment_fnc_fullHeal to enable/disable the full heal message that shows in the medical GUI. Should that be a separate PR after this or just do it in one?

Figured I'd just include what I meant, commit can just be reverted if it should be a separate PR