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>

src/po/vim.pot

@@ -8,7 +8,7 @@ msgid ""
 msgstr ""
 "Project-Id-Version: Vim\n"
 "Report-Msgid-Bugs-To: vim-dev@vim.org\n"
-"POT-Creation-Date: 2025-09-21 18:48+0000\n"
+"POT-Creation-Date: 2025-09-22 19:04+0000\n"
 "PO-Revision-Date: YEAR-MO-DA HO:MI+ZONE\n"
 "Last-Translator: FULL NAME <EMAIL@ADDRESS>\n"
 "Language-Team: LANGUAGE <LL@li.org>\n"
@@ -2220,10 +2220,16 @@ msgstr ""
 msgid " SPACE/d/j: screen/page/line down, b/u/k: up, q: quit "
 msgstr ""
 
+msgid "W24: Clipboard register not available. See :h W24"
+msgstr ""
+
 msgid "W23: Clipboard register not available, using register 0"
 msgstr ""
 
-msgid "W24: Clipboard register not available. See :h W24"
+msgid "W23: Clipboard register + not available, using register 0"
+msgstr ""
+
+msgid "W23: Clipboard register * not available, using register 0"
 msgstr ""
 
 msgid "Question"