window: Remove duplicated function declaration
window: Remove internal recalc_window_type / recalc_window_features

Just use the public symbols for them.
window: Use window-props interface to load role/net_wm_type on init
Start moving X11-specific code to window-x11.c

The goal here is to make MetaWindow represent a toplevel, managed window,
regardless of if it's X11 or Wayland, and build an abstraction layer up.
Right now, most of the X11 code is in core/ and the wayland code in wayland/,
but in the future, I want to move a lot of the X11 code to a new toplevel, x11/.