Clicking on a triangle in the files list should expand/collapse it #5088
Description
Is your feature request related to a problem? Please describe.
When I want to expand/collapse trees in the files view, I cannot do so with entirely with the mouse as clicking on the triangles does nothing other than select the line.
Describe the solution you'd like
Clicking on a triangle that is expanded should collapse that tree. Clicking on a triangle that is collapsed should expand that tree (to put it another way, it should work the same as clicking any part of that line and then pressing Return).
If I click on the triangle next to configure_firefox in the first picture, it should look like the second picture (and vice versa).
Describe alternatives you've considered
As mentioned above, clicking on the line and then pressing Return works. As my trackpad is to the right of the keyboard, though, and the Return key is also on the right, it means moving my hands back and forth (I guess this isn't such an issue with laptop trackpads :)
Additional context
