Rename "[Mm]ethod(s)" to "[Ff]unction(s)"

Only methods as programming functions are affected. Besides renaming
some actions like "Switch Between Function Declaration/Definition" this
mostly touches (api) code comments.

This is a follow-up patch to commit 872bfb7.

Change-Id: Icb65e8d73b59a022f8885b14df497169543a3b92
Reviewed-by: hjk <hjk121@nokiamail.com>

src/plugins/coreplugin/fileiconprovider.cpp

@@ -57,7 +57,7 @@ using namespace Utils;
         own overlay icon handling (Mac/Windows).
 
   Plugins can register custom overlay icons via registerIconOverlayForSuffix(), and
-  retrieve icons via the icon() method.
+  retrieve icons via the icon() function.
   */
 
 // Cache icons in a list of pairs suffix/icon which should be faster than