You'll never believe this. Clicking on the dropdown button on a ComboBox
doesn't set `e.Tapped = true`. It bubbles up, and lands in our `Pane`'s
`Border`'s tapped handler. And in there, we yeet focus to the first
content. We end up stealing focus from the combobox, and then the
combobox doesn't actually open its dropdown.
So yea we can just fix that. Easy enough.
Closes#17062
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Co-authored-by: Dustin L. Howett <duhowett@microsoft.com>
Co-authored-by: Leonard Hecker <lhecker@microsoft.com>