patch 8.2.0869: it is not possible to customize the quickfix window contents

Problem:    It is not possible to customize the quickfix window contents.
Solution:   Add 'quickfixtextfunc'. (Yegappan Lakshmanan, closes #5465)
diff --git a/runtime/doc/options.txt b/runtime/doc/options.txt
index d4d8787..82b91a6 100644
--- a/runtime/doc/options.txt
+++ b/runtime/doc/options.txt
@@ -5901,6 +5901,21 @@
 	This option cannot be set from a |modeline| or in the |sandbox|, for
 	security reasons.
 
+						*'quickfixtextfunc'* *'qftf'*
+'quickfixtextfunc' 'qftf'	string (default "")
+			global
+			{only available when compiled with the |+quickfix|
+			feature}
+	This option specifies a function to be used to get the text to display
+	in the quickfix and location list windows.  This can be used to
+	customize the information displayed in the quickfix or location window
+	for each entry in the corresponding quickfix or location list.  See
+	|quickfix-window-function| for an explanation of how to write the
+	function and an example.
+
+	This option cannot be set from a |modeline| or in the |sandbox|, for
+	security reasons.
+
 						*'quoteescape'* *'qe'*
 'quoteescape' 'qe'	string	(default "\")
 			local to buffer