[overlays] Fix overlay slowness when huge result is displayed

[alexander-yakushev]

Since calling string-width on a big string is very slow, displaying a big overlay (that we truncate later anyway) induces an unnecessary delay.

Here, I solve this by checking first for a too big of a result (10000 characters) that we certainly definitely going to truncate.

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• You've updated the changelog (if adding/changing user-visible functionality)

[bbatsov]

Here, I solve this by checking first for a too big of a result (10000 characters) that we certainly definitely going to truncate.

How did you pick this size? Overall - your approach seems reasonable, although probably I'd some comments explaining it in the code.

[alexander-yakushev]

I indeed just spitballed it. Now I think we can base the approximation on the screen width.

[alexander-yakushev]

Updated, no more magic values.

[bbatsov]

Yeah, that's much nicer. Thanks!