feat(options): add 'winpinned' to pin a window #39157

Problem:
- Unable to "pin" a window to prevent closing without specifically
  being targeted.
- :fclose closes hidden windows (even before visible windows).

Solution:
- Add 'winpinned' window-local option. When set, window is skipped by
  :fclose and :only. Pin the ui2 cmdline window (which should always be
  visible), so that it is not closed by :only/fclose.
- Skip over hidden (and pinned) windows with :fclose.

Co-authored-by: glepnir <glephunter@gmail.com>

src/nvim/options.lua

@@ -10713,6 +10713,19 @@ local options = {
       type = 'number',
       varname = 'p_wmw',
     },
+    {
+      abbreviation = 'wp',
+      defaults = false,
+      desc = [=[
+        If enabled, the window is pinned and will not be closed by |:only|
+        and |:fclose|. Only commands specifically targeting the window can
+        close it.
+      ]=],
+      full_name = 'winpinned',
+      scope = { 'win' },
+      short_desc = N_('prevent closing window with :only and :fclose'),
+      type = 'boolean',
+    },
     {
       abbreviation = 'wiw',
       cb = 'did_set_winwidth',