patch 8.1.2011: more functions can be used as methods

Problem:    More functions can be used as methods.
Solution:   Make various functions usable as a method.  Make the window
            command test faster.

runtime/doc/eval.txt

@@ -9606,6 +9606,8 @@ tabpagebuflist([{arg}])					*tabpagebuflist()*
 			endfor
 <		Note that a buffer may appear in more than one window.
 
+		Can also be used as a |method|: >
+			GetTabpage()->tabpagebuflist()
 
 tabpagenr([{arg}])					*tabpagenr()*
 		The result is a Number, which is the number of the current
@@ -9628,6 +9630,9 @@ tabpagewinnr({tabarg} [, {arg}])			*tabpagewinnr()*
 		    tabpagewinnr(4, '$')    " number of windows in tab page 4
 <		When {tabarg} is invalid zero is returned.
 
+		Can also be used as a |method|: >
+			GetTabpage()->tabpagewinnr()
+<
 							*tagfiles()*
 tagfiles()	Returns a |List| with the file names used to search for tags
 		for the current buffer.  This is the 'tags' option expanded.
@@ -9676,6 +9681,9 @@ taglist({expr} [, {filename}])				*taglist()*
 		located by Vim. Refer to |tags-file-format| for the format of
 		the tags file generated by the different ctags tools.
 
+		Can also be used as a |method|: >
+			GetTagpattern()->taglist()
+
 tan({expr})						*tan()*
 		Return the tangent of {expr}, measured in radians, as a |Float|
 		in the range [-inf, inf].