[WIP] Just to look at diff.

[DaveDavenport]

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[lbonn]

@DaveDavenport

Big outline:

What I did not want was to just add #ifdef of ifs in every function 😄

• xcb.c is renamed to display.c and the two implementations are in xcb/display.c and wayland/display.c. display-internal.h describes the interface they implement and plain display.c just proxies between the two.
• the split of view.c is not as clean: generic parts are kept in view.c but everything that was xcb-specific or differed too much from wayland was moved in xcb/view.c and wayland/view.c. The functions which are proxied this way are at the bottom of view.c
• there are actually a small number of ifdefs in view.c for some simple cases

For view, ideally wayland/view.c and xcb/view.c should disappear and some of their functionality can be moved to the corresponding display.c and/or another object.
I haven't reviewed exactly what could be put in common recently but I suspect there are at least some low hanging fruits.

Though they sizeable, around 1000 lines for xcb and half for wayland and both display.c are ~2000 lines. So, moving everything there would probably make a mess.