feat: publicize menu structures/methods

[Krzyhau]

MonoMod gives a way of making private/protected stuff from original binaries public. We should take advantage of that and make menu functions and structures open for modders. This would make creating custom menus for mods significantly easier.

[Jenna1337]

Looking at how HAT installs its in-game menu, it seems the only things we need publicized are the classes FezGame.Components.MainMenu, FezGame.Components.MenuBase, FezGame.Structure.MenuLevel, and FezGame.Structure.MenuItem<T> and the interface FezGame.Structure.MenuItem.
All the relevant methods, properties, and fields we need appear to be marked as either public or protected, so they shouldn't need to be changed.
Of course, we will still need a hook for MenuBase.Initialize()