fix: resolve /live channel liveness using their channel ID

[KleberPF]

This fix for #5158 uses the TwitchChannel roomId() as the message id when sending live messages (TwitchMessageBuilder::liveMessage and TwitchMessageBuilder::liveSystemMessage). I wasn't able to replicate the same logic for live messages sent through NotificationController (I couldn't find a way to access the TwitchChannel from there), so I went with the other option of using a case insensitive string compare. I accept any ideas on how I could do this better, especially the NotificationController bit.

(felanbird): Fixes #5158

[Felanbird]

changelog.md entry
- Bugfix: Fixed an issue where channels who were live before you opened Chatterino, didn't always get greyed-out in the `/live` tab when they went offline. (#5172)

[Felanbird]

This seems to work as expected, so far 3 of my channels loaded before displayName capitalization was obtained, have correctly been greyed-out in the /live tab when they went offline

[KleberPF]

Thanks for the review. Should I add a commit with the changelog entry?

[Felanbird]

Thanks for the review. Should I add a commit with the changelog entry?

if you want, otherwise pajlada will do it on the weekend (and maybe move my comma)

[KleberPF]

Added a commit because QString::compare returns 0 when the strings are equal

[pajlada]

Little bit hard to test but it seems to work as expected - thank you!

[pajlada]

Thank you! As a first-time contributor, you can now add yourself to the contributors list that's shown inside the About page in Chatterino.

If you want this, you can open a new PR where you modify the resources/contributors.txt file and add yourself to the list. Make sure to read the comments at the top for instructions.