Tab context not transferred to image upload dialog

[ArtOfCode-]

meta:293904

When uploading an image via the toolbar button, tab context is not transferred to the modal, resulting in the Tab key cycling elements on the background page rather than the modal.

[superplane39]

The dialog also doesn't close when you press the esc key, which is also an issue and should be fixed at the same time if possible.

[cellio]

New meta post about esc: https://meta.codidact.com/posts/293908

(I'm assuming we'll do it as part of this, per the previous comment. If not, need to spin off a separate issue for it.)

[Oaphi]

Note to self: Esc is supposed to be working, we are just using the keypress deprecated event.