ColorDialog: Implement the ColorInputs.qml component in C++

The ColorDialog will be added to the QtQuick.Dialogs module in 6.4

The ColorDialog has a few controls (a ComboBox and some TextFields), inside of a layout, that shows the color values of the currently selected color. 
These TextFields can be edited to modify the currently selected color too.

In the current state, they are all declared in qml, and use javascript functions as signal handlers. We want to avoid having to do any logic in javascript, which is why I should write most of this logic in C++.

ColorInputs.qml is also incredibly buggy at the moment. The different items will not always get the correct size that they should.

With the Imagine style  the ComboBox will get the same size as the TextFields, which is not what we want. The TextFields should get more space allocated to them, than the ComboBox.