QmlDesigner.StatesEditor: using TextField

There are a couple of issues with TextInput.
So we use TextField instead.

Focus issues are still an issue even if using controls.

Task-number: QTCREATORBUG-6278

Change-Id: I005eda1565e0a3fa002baeffaab9c12662f90288
Reviewed-by: Thomas Hartmann <Thomas.Hartmann@digia.com>