Tree Don't consume mouse event by collapse arrow which isn't shown

[kleonc]

Collapse/folding arrow is shown only when TreeItem has children (has the first child) and it should handle a mouse event only if it's actually visible.

[KoBeWi]

It is some improvement, but what exactly does this change? I don't see any difference in behavior.

[kleonc]

It is some improvement, but what exactly does this change?

It makes mouse events not being handled/consumed by an invisible collapse/folding arrow.

I don't see any difference in behavior.

For reference: I've noticed this wrong behavior because of #55774 (I'm mentioning this PR in #55774 (comment)).
For example open Editor -> Manage Editor Features... dialog. Currently for tree items with no children checkboxes can be toggled by clicking on the left from the invisible collapse arrow (you can test it yourself) but not by clicking over that invisible arrow (because it handles the event):


But if the checkbox (or anything else) is supposed to handle mouse event on the left then the invisible arrow shouldn't block it. And that's what this PR is fixing. With this PR:

And this PR isn't really about the checkboxes and whether it makes sense to toggle them by clicking to the left from them (that's what #55774 is about). It's just an example. An invisible collapse/fold arrow shouldn't handle/consume mouse event over it no matter (as it's kinda nonexistent) what and that's what this PR is fixing.

[akien-mga]

Thanks!