move plugin text codecs to QtCore

move plugin text codecs to QtCore

Having plugin text codecs adds considerable complexity to
configuring Qt. The plugin interface is designed for optional
features, but text codecs tend to be used for essential functions.
A dramatic example is loading a codec plugin from a file whose path
needs to be converted by the codec.

Codec plugins can also be a nuisance to builders of applications
linking to static Qt. This is because the application might need
to explicilty import the static codec plugins which are actually
dependencies of QtCore.

For these reasons, it has been decided not to have text codec plugins
any longer.

Change-Id: Ic6c80a9c949bd42e881e932d1edae23fe4fe4c88
Reviewed-by: Lars Knoll <lars.knoll@nokia.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>