patch 8.2.3619: cannot use a lambda for 'operatorfunc'

Problem:    Cannot use a lambda for 'operatorfunc'.
Solution:   Support using a lambda or partial. (Yegappan Lakshmanan,
            closes #8775)
diff --git a/runtime/doc/options.txt b/runtime/doc/options.txt
index a0bbd3b..b5bcceb 100644
--- a/runtime/doc/options.txt
+++ b/runtime/doc/options.txt
@@ -371,6 +371,17 @@
 ":setlocal" on a global option might work differently then.
 
 
+						*option-value-function*
+Some options ('completefunc', 'imactivatefunc', 'imstatusfunc', 'omnifunc',
+'operatorfunc', 'quickfixtextfunc' and 'tagfunc') are set to a function name
+or a function reference or a lambda function.  Examples:
+>
+	set opfunc=MyOpFunc
+	set opfunc=function("MyOpFunc")
+	set opfunc=funcref("MyOpFunc")
+	set opfunc={t\ ->\ MyOpFunc(t)}
+<
+
 Setting the filetype
 
 :setf[iletype] [FALLBACK] {filetype}			*:setf* *:setfiletype*
@@ -5623,7 +5634,9 @@
 'operatorfunc' 'opfunc'	string	(default: empty)
 			global
 	This option specifies a function to be called by the |g@| operator.
-	See |:map-operator| for more info and an example.
+	See |:map-operator| for more info and an example.  The value can be
+	the name of a function, a |lambda| or a |Funcref|. See
+	|option-value-function| for more information.
 
 	This option cannot be set from a |modeline| or in the |sandbox|, for
 	security reasons.
@@ -6023,8 +6036,9 @@
 	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. The value can be the name of a function or a
-	lambda.
+	function and an example.  The value can be the name of a function, a
+	|lambda| or a |Funcref|. See |option-value-function| for more
+	information.
 
 	This option cannot be set from a |modeline| or in the |sandbox|, for
 	security reasons.