bug#64200: Netsurf very frequently freezes when editing text (Harfbuzz issue?)

[Csepp]

Like the title says.  It never happens when just browsing, but happens
very frequently (like a minute after starting to type) when editing
text, at least on Brutaldon, but maybe on other sites too.

I noticed that our Harfbuzz package is two entire major releases behind.
Maybe there are bugfixes in the latest one that we could use?

I tried building it but it froze up my laptop for some reason (rather
strange, even if it runs out of memory it should just be killed by
earlyoom) so I haven't attempted to test this theory yet.

Is there any particular reason Harfbuzz wasn't covered by the last
core-updates?  If it turns out to be a bug in it, what would be the best
way to proceed?