Desired combobox improvements

[guaje]

Is your feature request related to a problem? Please describe.

Having our combobox UI element is excellent, and despite all the customization options it provides, it would be great if the following concerns could be improved:

Describe the solution you'd like

1. It always starts in expanded mode, as seen in the following image. When creating apps with several UI elements, it would be better if the comboboxes could be initiated in a collapsed mode and expanded only under users' requests.

2. Positioning a combobox on a panel is not intuitive due to the previously described situation.

3. Even when one option is selected and the combobox is collapsed, UI elements behind the combobox panel cannot be clicked. For example, the DoubleSlider in the following image.

[skoudoro]

Point 3 seems to be a common issue for multiple UI. the hidden background (usually a panel2D) should be resized or disabled.