Re-writes clipboard data handling in X11 to an on demand approach where
data can be produced on request instead of storing it in X11 properties
on the window.
Primary selection has been changed to mimic this behavior even though
it's only possible to use it for text as of now.
Re-writes the clipboard data handling in wayland to an on demand
solution where callbacks are provided to generate/provide the clipboard
data when requested by the OS.
This takes care of the last set of void functions that could
potentially be shifted to instead return an int indicating success and
setting an error in case of an error.
Linus Probert