Update CharacterController3D for modularity

[Blade67]

The current CharacterController3D requires constant updating when adding new features. This proposal proposes to update the behavior in favor of a more dynamic approach.

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Signals

Instead of individually creating new signals for each ability inside of the CharacterController3D class, either create them dynamically using the native add_user_signal function, or declare them inside the ability and make the CharacterController3D connect to them dynamically.

Properties

Properties should be ability-bound, thus visible from the editor under the abilities_path array, when selecting the ability. This would however require the abilities to be resources, potentially making this a major undertaking.

Emitters

Emitting signals should be done from within abilities and not on the CharacterController3D.

TL;DR

Each ability should only take care of themselves, independently (or co-dependent of another's ability by connecting to it directly) of others. This allows more complex behavior and abilities being more than just movement related. (ie. interaction handling, etc.)