patch 8.2.1241: cannot use getbufinfo() as a method

Problem:    Cannot use getbufinfo() as a method.
Solution:   Support using getbufinfo() as a method. (closes #6458)

runtime/doc/eval.txt

@@ -4929,8 +4929,11 @@ getbufinfo([{dict}])
 <
 		To get buffer-local options use: >
 			getbufvar({bufnr}, '&option_name')
-
 <
+		Can also be used as a |method|: >
+			GetBufnr()->getbufinfo()
+<
+
 							*getbufline()*
 getbufline({expr}, {lnum} [, {end}])
 		Return a |List| with the lines starting from {lnum} to {end}