Merge #22382 has('gui_running')

runtime/doc/builtin.txt

@@ -3867,6 +3867,7 @@ has({feature})	Returns 1 if {feature} is supported, 0 otherwise.  The
 			clipboard	|clipboard| provider is available.
 			fname_case	Case in file names matters (for Darwin and MS-Windows
 					this is not present).
+                        gui_running	Nvim has a GUI.
 			iconv		Can use |iconv()| for conversion.
 			linux		Linux system.
 			mac		MacOS system.

runtime/doc/news.txt

@@ -179,6 +179,11 @@ The following new APIs or features were added.
 
   Additionally |TSNode:range()| now takes an optional {include_bytes} argument.
 
+• |nvim_list_uis()| reports all |ui-option| fields.
+
+• Vim's `has('gui_running')` is now supported as a way for plugins to check if
+  a GUI (not the |TUI|) is attached to Nvim. |has()|
+
 ==============================================================================
 CHANGED FEATURES                                                 *news-changes*
 

runtime/doc/ui.txt

@@ -53,9 +53,8 @@ with these (optional) keys:
 - `term_name`		Sets the name of the terminal 'term'.
 - `term_colors`		Sets the number of supported colors 't_Co'.
 - `term_background`	Sets the default value of 'background'.
-- `stdin_fd`		Read buffer from `fd` as if it was a stdin pipe.
-			This option can only used by |--embed| ui on startup.
-			See |ui-startup-stdin|.
+- `stdin_fd`		Read buffer 1 from this fd as if it were stdin |--|.
+			Only from |--embed| UI on startup. |ui-startup-stdin|
 - `stdin_tty`		Tells if `stdin` is a `tty` or not.
 - `stdout_tty`		Tells if `stdout` is a `tty` or not.