Refactor text formatting functions

[marcustyphoon]

Description

Should result in no functional changes. This extracts some utility functions that are used in the modals of various scripts into a utility file to reduce repetition.

Open to bikeshedding (different file name, interface.js, modals.js, whatever).

Testing steps

[AprilSylph]

if you want bikeshedding... here's some extreme bikeshedding for you...!

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I feel like trying to follow XKit 7's pattern of grouping utils just for the sake of grouping them was kinda silly, and I regret doing it. Rather than think up names for collections of utils which don't even share any code, I think the easier and clearer thing is to have one export per util file, e.g.

• src/util/construct_relative_time_string.js
  • Defines thresholds
  • Defines relativeTimeFormat
  • Exports constructRelativeTimeString
• src/util/date_time_format.js
  • Exports dateTimeFormat
• src/util/elements_as_list.js
  • Exports elementsAsList

Of course, this pattern doesn't work for util files which export several interdependent values (like user_blogs.js), but at least that way we're only doing the group-naming work when it's actually necessary.

[marcustyphoon]

Spoken like a true developer-whose-project-at-work-uses-a-bundler, I kid, I kid, don't sue me, I'm innocent :P

I certainly don't think I would go unequivocally to the opposite extreme, where one winds up with a folder full of function names in alphabetical order. If a set of functions will usually be used together or would need all need to be refactored at the same time, I think it makes sense to be able to find one from the other via context. But yeah, I think there's certainly places for it. interface.js is pretty much a grab bag, iirc. I feel like it might make sense to put the functions that take an NPF object together (might have to add one to normalize community posts?)