Prevent usernames from overflowing the reactions hover-list (resolves #737)

What does this PR do?

Crop long usernames that would otherwise overflow the reactions list. An ellipses is used to indicate truncation.

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added bugfrontend label

I'm surprised the nowrap option doesn't work like that considering the CSS is basically 1:1 with the nowrap option in the MFM component the only difference is the white-space option

resolved all threads

approved this merge request

enabled an automatic merge when all merge checks for a1375c8a pass

approved this merge request

merged

mentioned in commit 30937074