use wl_container_of() instead of data in some functions

add some comments

inline input_device in virtualkeyboard()

fix idle inhibitor check

previously we tried to get a client from the surface and then compare it with
the excluded surface, if we cannot get a client from the surface (e.g: a layer
surface) it just ignored all the next idle inhibitors no matter what

What I have should done is just checking if the excluded surface is equal to
the current idle inhibitor's surface and continue in case it is.

fix exclusive zone of unmapped layer surfaces

Fixes: https://github.com/djpohly/dwl/issues/302

resize the fullscreen background when resize the client

define _POSIX_C_SOURCE through CPPFLAGS

like dwm

fix condition that always evaluate to false in commitlayersurfacenotify()

remove obsolete check of c->mon in fullscreennotify()

since 19a8a095ebe782065903b9a03670560371302206 it's checked in setfullscreen()

set `c->prev` in setmon() and not in mapnotify()

only enable/disable clients from the specified monitor in arrange()

also fix a crash when m is null, this can only happen when selmon is NULL

set c->prev in mapnotify()

Closes: #300

don't arrange layers on disabled monitors

call setfullscreen() in setmon()

this will help when sending to another monitor a fullscreen client
and also will prevent a crash when a client request fullscreen when it has no monitor

prevent segfault when destroying monitors

also don't count unmapped surfaces for exclusive zone
and exclusive_focus is now of type `void *`

Revert "Revert "various improvements to layer surface""

This reverts commit c017916d35795cf85e5181907f5e97a1d702612a.

Revert "various improvements to layer surface"

see https://github.com/djpohly/dwl/issues/289#issuecomment-1231287114

This reverts commit 226051974060746d02d787ac1ef70b6267ee51b4.

various improvements to layer surface

- remove various useless assignments of layersurface->mon
- styles changes
- do not set wlr_layer_surface->output to NULL at destroy

conform the idle inhibitor protocol

previously we disable idle tracking simply due to the fact that it exist

new function to notify keyboard enter