Debugger: Implement stack frame switching with LLDB

Change-ID: I6efed5ffdccc5ce0aa13b1e7296137396ca28efe
Reviewed-by: hjk <hjk121@nokiamail.com>
CppEditor: Hide "Assign to Local Variable" if signatures don't match

Task-number: QTCREATORBUG-9321

Change-Id: I31ac75a480b30ef26f343557088c4bbe5e95c4c6
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@digia.com>