core: reimplement Wayland support

[joshua-holmes]

Utilized previous Wayland implementation as a base, but made the following changes:

• used separate structs for Linux and Wayland/X11, then placed properties in more-or-less the correct place. e.g. properties that belong to Wayland are in Wayland.zig. Properties that belong to any Linux implementation belong in Linux.zig. I did not do this perfectly, but it can be iterated on later (especially after X11 is implemented).
• plugged Wayland into the new event loop
• namespaced all of the listener code (registry_listener for example) because all the listeners consist of one or more functions, and an actual listener with is an instance of a struct that holds pointers to those functions. The functions aren't used anywhere else, so it made sense to me to package the listener struct and it's functions together under one namespace. Each listener has it's own namespace.
• grouped the xkb modifier indices into their own struct because it looked cleaner to have them grouped, and they are always used together anyway
• removed pieces of the old Wayland implementation that I was fairly confident were not necessary, e.g. calling wl_proxy_set_tag looked unnecessary because wl.tag was never set (which means maybe null was getting passed in?) and it doesn't look to me like that tag was never used anywhere else to reference the surface.

libwaylandclient.wl_proxy_set_tag(@ptrCast(wl.surface), @ptrCast(&wl.tag));

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