add attribute for spoilers

[catgirlinspace]

Hi, this is a start to #2839. I've never done iOS development before (outside of playing around with the templates in Xcode years ago) but I tried to follow what was already there. Currently the string has the spoilered parts get marked with the attribute but I have no idea how to actually hide them (I'm guessing I need a pill thing?).

Currently:
Element Web

Current Element X (spoilered text is shown as nothing)

This pull request currently (spoilered text is shown plain)

Leaving this as a draft for now while I figure out how to make it actually appear hidden. Also guessing maybe stuff for notifications would need changed to hide spoilered text? Any advice would be appreciated!

Pull Request Checklist

• I read the contributing guide.
• Pull request contains a changelog label.

UI changes have been tested with:

• iPhone and iPad simulators in portrait and landscape orientations.
• Dark mode enabled and disabled.
• Various sizes of dynamic type.
• Voiceover enabled.

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All committers have signed the CLA.

[sonarqubecloud]

Quality Gate passed

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[stefanceriu]

Nice start, thank you 🙏

Unfortunately this is indeed the easy part.

As you need the spoiler view to be interactive (so you can tap to show) your only option is a custom NSTextAttachment and their NSTextAttachmentViewProvider, which, as you noticed, we also use for mention pills.
I would however suggest you build the spoiler completely separate from all of that i.e. introduce a new type, a new provider and view.

I might also be a good idea to hold the spoiler text within the attribute so you can build the right size view.
Also, keep in mind that text can wrap and your spoiler should too. TextRenderer might prove useful.

[catgirlinspace]

Hi, sorry for the late reply--have been pretty busy.

Thank you for those pointers! I'll try implementing something soon-ish (whenever I have free time, have been pretty busy with uni) but I'll admit I don't have much confidence in myself with my lack of iOS experience :(