patch 8.2.1978: making a mapping work in all modes is complicated

Problem:    Making a mapping work in all modes is complicated.
Solution:   Add the <Cmd> special key. (Yegappan Lakshmanan, closes #7282,
            closes 4784, based on patch by Bjorn Linse)
diff --git a/runtime/doc/eval.txt b/runtime/doc/eval.txt
index c08b75b..3303cab 100644
--- a/runtime/doc/eval.txt
+++ b/runtime/doc/eval.txt
@@ -8660,6 +8660,7 @@
 		the following mappings: >
 			nnoremap <expr> GG ":echom ".screencol()."\n"
 			nnoremap <silent> GG :echom screencol()<CR>
+			nnoremap GG <Cmd>echom screencol()<CR>
 <
 screenpos({winid}, {lnum}, {col})				*screenpos()*
 		The result is a Dict with the screen position of the text