Fix PopupMenu unresponsive on right side of menu

[nathanfranke]

Bugsquad edit: Fixes #41762.

[akien-mga]

CC @EricEzaM

[EricEzaM]

Hi @nathanfranke, @akien-mga.

Unfortunately I cannot reproduce the issue on my PR... not sure what is going on - maybe it is a platform specific issue? Anyway, this PR breaks what this piece of code tries to solve - not selecting items when trying to select the scrollbar. See below video of my test.

So, the reason this code is required is because of the below situation. The scroll container just renders the scrollbar above the content. This is why I used the control rect initially, as it already accounts for the margin container. However, the scroll container rect would also work, as in my review below.

[EricEzaM]

These changes do simplify the code quite a bit, thanks for that! I have suggested 2 options below - either work on my system. A good way to test the scrollbar is by going to the below button and changing the file dialog filter, since it has so many options.

[nathanfranke]

I chose option "A" since it seemed more elegant 😄

[EricEzaM]

All good on my end after a test, thanks!

[akien-mga]

Also fixes #41762.

[akien-mga]

Thanks!