ui: Confirmation on exit from exec as long as socket has been opened

[philrenaud]

Resolves #19849

In an exec window context, navigating away from the page is not possible by in-page links, as there are none (besides Documentation, which opens in a new tab). Otherwise, closing the window by clicking exit, or using a keyboard shortcut like ctrl+w, ctrl+q, etc. is the most common method.

Unfortunately, some of those keyboard shortcuts are also used for in-terminal activity (like ctrl+w to delete a word in bash, or split a terminal in vim), and users' muscle memory may cause them to close a window, losing time and context along the way.

This PR adds a beforeunload handler to the exec terminal component, triggered whenever a socket is open and the user does an action that would close the parent tab/window. It will add a prompt asking the user if they meant to close it, and if they hit cancel or escape, it will bring their context back to the cursor in the terminal. Otherwise, the window will be closed.

[github-actions]

Ember Test Audit comparison

	main	f918170	change
passes	1548	1548	0
failures	0	0	0
flaky	0	0	0
duration	11m 10s 108ms	11m 13s 129ms	+03s 021ms

[lgfa29]

⌨️

[github-actions]

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