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/src/evalfunc.c b/src/evalfunc.c
index 2d88668..04967ef 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -2077,6 +2077,14 @@
 			ret_string,	    f_getbufoneline},
     {"getbufvar",	2, 3, FEARG_1,	    arg3_buffer_string_any,
 			ret_any,	    f_getbufvar},
+    {"getcellpixels",	0, 0, 0,	    NULL,
+			ret_list_any,
+#if (defined(UNIX) || defined(VMS)) && (defined(FEAT_EVAL) || defined(PROTO))
+	    f_getcellpixels
+#else
+	    NULL
+#endif
+			},
     {"getcellwidths",	0, 0, 0,	    NULL,
 			ret_list_any,	    f_getcellwidths},
     {"getchangelist",	0, 1, FEARG_1,	    arg1_buffer,