Document Player's Face and z_actor FaceChange functions

[fig02]

This PR does a few things:

• Introduces enums for various things related to links face
• Documents eyes and mouth textures
• Documents the FaceChange system in z_actor
• Changes FaceChange functions to use a struct instead of an array (looks much nicer)

FaceChange is only used by player, but it is documented generically. The system is pretty clearly designed to work for any actor. However the system isn't all that great (imo), so it makes sense why other actors didnt use it.

Naming Player's eyes/mouths and faces is quite hard. OoT3D confirms that they originally didn't bother naming them, they just numbered them. But that doesn't mean we cant try.

My omission of offset comments on enums and structs is my public protest of introducing them into our repo anymore cause I find them useless. But I will add them if someone asks me to 😄.

Thanks DarkEye for pulling oot3d info for me. And thanks Tharo for some help on understanding the FaceChange functions.