patch 9.1.0854: cannot get terminal cell size

Problem:  cannot get terminal cell size
Solution: add getcellpixels() function to return xpixel * ypixel
          cell size on terminal Unix (mikoto2000)

closes: #16004

Signed-off-by: mikoto2000 <mikoto2000@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/runtime/doc/builtin.txt b/runtime/doc/builtin.txt
index 67f447d..1c7814f 100644
--- a/runtime/doc/builtin.txt
+++ b/runtime/doc/builtin.txt
@@ -1,4 +1,4 @@
-*builtin.txt*	For Vim version 9.1.  Last change: 2024 Nov 10
+*builtin.txt*	For Vim version 9.1.  Last change: 2024 Nov 11
 
 
 		  VIM REFERENCE MANUAL	  by Bram Moolenaar
@@ -222,6 +222,7 @@
 getbufoneline({buf}, {lnum})	String	line {lnum} of buffer {buf}
 getbufvar({buf}, {varname} [, {def}])
 				any	variable {varname} in buffer {buf}
+getcellpixels()			List	get character cell pixel size
 getcellwidths()			List	get character cell width overrides
 getchangelist([{buf}])		List	list of change list items
 getchar([{expr}])		Number or String
@@ -3786,6 +3787,15 @@
 		Return type: any, depending on {varname}
 
 
+getcellpixels()						*getcellpixels()*
+		Returns a |List| of terminal cell pixel size.
+		List format is [xpixels, ypixels].
+		Only works on Unix. For gVim and on other systems,
+		returns [-1, -1].
+
+		Return type: list<Number>
+
+
 getcellwidths()						*getcellwidths()*
 		Returns a |List| of cell widths of character ranges overridden
 		by |setcellwidths()|.  The format is equal to the argument of