Add EoC ability to remove effect from specific body part

[furran]

Summary

Features "Add optional field "target_part" to EoC character effect 'remove_effect'"

Purpose of change

Adds EoC ability to remove effect from a specific body part, similar to how u_add_effect/npc_add_effect works.

Closes #70131

Describe the solution

Updated set_remove_effect and necessary functions to allow for selection of a body part. Just like it works in set_add_effect.
Also updated docs.

Describe alternatives you've considered

None

Testing

Drop this json file into data/effects_on_condition: furran_tests.json

1. Get in game. Give yourself the spells in furran_tests.json.
2. Use Test Bleed on yourself, check your wounds. Your head, torso and arms should be bleeding.
3. Use Test Cure Head on yourself. Check your wounds again. Only your head should have stopped bleeding.
4. Repeat 2 and 3 but instead target a debug monster.

Additional context