move QtQuick.Dialogs from qtdeclarative to qtquickcontrols

This will enable using Controls in the QML dialog implementations.
For now, Controls are used only as drop-in replacements for the
Button, Checkbox, and TextField which were custom implementations
in the qtdeclarative module before.

Change-Id: Ic79e9e8e5715a72ce51f4c724bfdfd33653300f2
Reviewed-by: Liang Qi <liang.qi@digia.com>