Fix tagline overflow

[micahmo]

Pull Request Description

This PR fixes an issue with taglines. Currently there is some logic to condense the tagline if it's very long. However, this logic performs a very simple string truncation, which can break the tagline if it truncates in the middle of markdown.

I fixed this issue by using a similar technique to the post body expander, so that the it is done by height, rather than characters. I also introduced a measurement, so the truncation only happens if the tagline is taller than a specified height. We might consider introducing this mechanism back into the post body (because I've seen cases where the body is short and the expander does almost nothing).

Review without whitespace.

Issue Being Fixed

Before

tagline_before.mp4

After

tagline_after.mp4

After -- short tagline still has no expander

Issue Number: N/A

Screenshots / Recordings

Checklist

• Did you update CHANGELOG.md?
• Did you use localized strings where applicable?
• Did you add semanticLabels where applicable for accessibility?

[hjiangsu]

LGTM!