Support multiple InputMethodContext callback connect by own signal

Support multiple InputMethodContext callback connect by own signal

InputMethodContext only support single EventReceivedSignal globaly, from 2018 years.

But we can have multiple InputMethodContext,
and each InputMethodContext could have there own signal to connect.

Since C# signal can only receive pointer data from C++, there should exist
some data conversion progress in csharp-binder code.

Until now, we only use single functor for it.
But now, let we allow to get-set this signal, key as pointer of signal.

After this patch, we can connect each InputMethodContext connect their own signals.

Change-Id: I6fe6794387e8ab80a1ddb346a2931929654b961c
Signed-off-by: Eunki, Hong <eunkiki.hong@samsung.com>