patch 9.1.1784: Wayland code can be improved

Problem:  Wayland code can be improved
Solution: Refactor Wayland Clipboard code (Foxe Chen).

This the second attempt to refactor the Wayland code base:
- Move clipboard code from wayland.c to clipboard.c
- Use C99 bool type
- Properly poll the Wayland display file descriptor
- Instead of checking if the data source is not NULL in order to
  determine if a selection event comes from us, use a special mime type
  to identify selection events coming from ourselves. The problem with
  the previous approach is that race conditions may occur.
- Put the focus stealing code under a new feature "wayland_focus_steal"
- Use ELAPSED_* macros instead of gettimeofday()
- Pass tests
- Reimplement commented out code
- Update docs
- Make Wayland clipboard behaviour more in line with X11 when connection
  is lost
- add missing malloc checks and possible memory leaks + refactored some
  tests.

closes: #18324

Signed-off-by: Foxe Chen <chen.foxe@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

runtime/doc/builtin.txt

@@ -1,4 +1,4 @@
-*builtin.txt*	For Vim version 9.1.  Last change: 2025 Sep 21
+*builtin.txt*	For Vim version 9.1.  Last change: 2025 Sep 22
 
 
 		  VIM REFERENCE MANUAL	  by Bram Moolenaar
@@ -13194,7 +13194,9 @@ vreplace		Compiled with |gR| and |gr| commands. (always true)
 vtp			Compiled for vcon support |+vtp| (check vcon to find
 			out if it works in the current console).
 wayland			Compiled with Wayland protocol support.
-wayland_clipboard	Compiled with support for Wayland selections/clipboard
+wayland_clipboard	Compiled with support for Wayland clipboard.
+wayland_focus_steal	Compiled with support for Wayland clipboard focus
+			stealing.
 wildignore		Compiled with 'wildignore' option.
 wildmenu		Compiled with 'wildmenu' option.
 win16			old version for MS-Windows 3.1 (always false)

runtime/doc/gui_x11.txt

@@ -1,4 +1,4 @@
-*gui_x11.txt*   For Vim version 9.1.  Last change: 2025 Sep 02
+*gui_x11.txt*   For Vim version 9.1.  Last change: 2025 Sep 22
 
 
 		  VIM REFERENCE MANUAL    by Bram Moolenaar
@@ -714,6 +714,8 @@ output a warning:
 
   Warning: Clipboard register not available, using register 0 ~
 
+Note: This also applies to the Wayland clipboard feature as well.
+
 								*W24*
 Vim comes in different flavors, from a tiny build, that just tries to be
 compatible to original Vi, to enhanced builds which include many improvements

runtime/doc/options.txt

@@ -1,4 +1,4 @@
-*options.txt*	For Vim version 9.1.  Last change: 2025 Sep 20
+*options.txt*	For Vim version 9.1.  Last change: 2025 Sep 22
 
 
 		  VIM REFERENCE MANUAL	  by Bram Moolenaar
@@ -10204,7 +10204,8 @@ A jump table for the options with a short description can be found at |Q_op|.
 				*'wlsteal'* *'wst'* *'nowlsteal'* *'nowst'*
 'wlsteal' 'wst'		boolean  (default off)
 			global
-			{only when the |+wayland_clipboard| feature is included}
+			{only when the |+wayland_focus_steal| feature is
+			included}
 	When enabled, then allow Vim to steal focus by creating a temporary
 	surface, in order to access the clipboard.  For more information see
 	|wayland-focus-steal|.

runtime/doc/tags

@@ -1541,6 +1541,7 @@ $quote	eval.txt	/*$quote*
 +vtp	various.txt	/*+vtp*
 +wayland	various.txt	/*+wayland*
 +wayland_clipboard	various.txt	/*+wayland_clipboard*
++wayland_focus_steal	various.txt	/*+wayland_focus_steal*
 +wildignore	various.txt	/*+wildignore*
 +wildmenu	various.txt	/*+wildmenu*
 +windows	various.txt	/*+windows*

runtime/doc/various.txt

@@ -1,4 +1,4 @@
-*various.txt*   For Vim version 9.1.  Last change: 2025 Sep 02
+*various.txt*   For Vim version 9.1.  Last change: 2025 Sep 22
 
 
 		  VIM REFERENCE MANUAL    by Bram Moolenaar
@@ -528,6 +528,9 @@ T  *+vreplace*		|gR| and |gr|
    *+vtp*		on MS-Windows console: support for 'termguicolors'
 N  *+wayland*		Unix only: support for the Wayland protocol.
 N  *+wayland_clipboard*	Unix only: support for Wayland selections/clipboard.
+N  *+wayland_focus_steal*
+			Unix only: support for Wayland clipboard on
+			compositors without a data control protocol
 T  *+wildignore*	'wildignore'  Always enabled since 9.0.0278
 T  *+wildmenu*		'wildmenu'  Always enabled since 9.0.0279
 T  *+windows*		more than one window; Always enabled since 8.0.1118.

runtime/doc/wayland.txt

@@ -1,4 +1,4 @@
-*wayland.txt*   For Vim version 9.1.  Last change: 2025 Sep 15
+*wayland.txt*   For Vim version 9.1.  Last change: 2025 Sep 22
 
 
 		  VIM REFERENCE MANUAL    by Bram Moolenaar
@@ -105,7 +105,8 @@ To solve this problem, Vim implements a way of gaining focus in order to
 access the clipboard, by creating a temporary transparent top-level surface.
 This is by default disabled and can be enabled via the 'wlsteal' option.
 Moreover, a seat that has a keyboard is also required, see 'wlseat', and the
-xdg-shell protocol must be available.
+xdg-shell protocol must be available. Additionally, Vim must be compiled with
+the |+wayland_focus_steal| feature.
 
 Note that this method can have several side effects from the result of focus
 stealing.  For example, if you have a taskbar that shows currently opened apps