ComboBox stretching is buggy

[pixelzoom]

ComboBox layout is currently buggy when stretched.

For example, in Kepler's Laws, TargetOrbitsComboBox implements this combobox:

The designer would like to stretch the combobox to fill the width of the panel. Adding this to default options for TargetOrbitsComboBox:

      layoutOptions: {
        stretch: true
      },

... gets us partway there:

But the above layout is buggy. Specifically:

• The right part of the button (arrow) should not resize.
• The left part of the button (the selected items) should resize, and the selected item should remain left aligned.
• The listbox should resize to match the width of the left part of the button.

Assigning to @jonathanolson, since he recently revised the layout for ComboBox.

For the requirement in Kepler's Law, I advised @AgustinVallejo to push back on the design requirement. So @DianaTavares (the designer) decision on whether this is required will determine the priority of this issue, and whether it's blocking.

[DianaTavares]

I don't love how it looks, but it is functional. For Kepler, then it is ok if the combo box is centered and doesn't follow my design.