Implement field getters as hooks

See https://github.com/makspll/bevy_mod_scripting/blob/main/crates/languages/bevy_mod_scripting_rhai/src/lib.rs for implementing a language UI.

See https://docs.rs/bevy_mod_scripting/0.16.0/bevy_mod_scripting/attr.script_bindings.html and https://github.com/makspll/bevy_mod_scripting/blob/main/examples/game_of_life.rs#L174-L182 for usage (this is how we should actually define the builtins in the quake-specific server crate).

*TODO*: How do we differentiate between getters and builtins?

*TODO*: Do we auto-generate getters for individual fields of vectors based on their index?

Start with crates/languages/bevy_mod_scripting_rhai/src/lib.rs, then compare the script_bindings documentation and examples/game_of_life.rs lines 174-182. Resolve how getters differ from builtins and whether vector fields should be generated by index; done means field getter hooks are implemented and the builtins can be defined in the Quake-specific server crate.

Written by the indexing model from the issue text.