Context Menu API rework

[PinewoodPip]

The context menu API is incredibly old at this point (2 years, almost) and needs modernizing to adhere to current standards. All current functionality should be kept.

• Annotate all methods and structures
• Change structures to use current naming conventions for fields (currently they are all in lowercase which is cringe)
• Change the way menus are declared and hooked, as current solution is a bit clunky. Allow the user to pass a default context menu with any call to open it. Then have a hook to modify the menu.

The UI currently replaces the vanilla one. Ideally it should be turned into a Generic UI, however the hardcoded quirks of the vanilla context menu could make it difficult to use an overlay. The change to Generic can be made later (it wouldn't affect the API).