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>
CppEditor: Harden FunctionHelper::overrides

Task-number: QTCREATORBUG-10333

Change-Id: I2ba7e0d5b8b8eb856445e737dfa21ec8a543f85d
Reviewed-by: Orgad Shaneh <orgads@gmail.com>
Reviewed-by: Erik Verbruggen <erik.verbruggen@digia.com>