replace newlines in desktop notifs with spaces instead of just removing them

[MightyPork]

fix desktop notifications removing spaces without any replacement, causing words to be joined
this bug was there for several months now, i finally got enough of it lol

added all possible newline types, seems to have no negative effects and better to have it more general just in case imo

[Gargron]

I'm not sure if desktop notifications honour \n newlines or not, but if they do, wouldn't it be better to replace br with those

[MightyPork]

I think it supports \n, but it doesn't seem to be very reliable - the w3 example page uses " \n" (for compatibility?)

this has advantages:

• multiline toots won't show ridiculously huge notifications
• it's easy (textContent seems to discard newlines, so some workaround would be needed)
• it collapses multiple newlines / spaces to a single space

[sorin-davidoi]

This also affects push notifications (#4860) - the same fix may be required, but in the backend (I think this line is responsible). @MightyPork do you think you can address this as well?

[MightyPork]

@sorin-davidoi I don't know ruby, so it'd be something horrible glued together from stackoverflow, better if we merge this first and you can add that later i think

[sorin-davidoi]

I don't know ruby, so it'd be something horrible glued together from stackoverflow

That would not be something bad, as that is how the push notifications were implemented 😄