refactor: Ignores and Replacements

[Nerixyz]

Refactors the replacement of ignores. I noticed two additional bugs:

• Kappa Keepo → Keepo Kappa wouldn't add emotes
• Regex lookahead/-behind wouldn't work

Fixes #2617.
The limit for replacements is 128, if this is reached, the message will be replaced with:
Too many replacements - check your ignores!
I couldn't see a good use-case where these many iterations would make sense.

Additionally:

• Merged regex and non-regex replacements
• Use SizeType to support both Qt 5 and 6 (this should be done for more stuff)
• Added comments to std algorithm
• Removed a few mutables
• Use tokenize in Qt 6

It's a bit unfortunate that we still have QRegularExpression emoteregex("\\b" + emote.name.string + "\\b", ..) which will always be cold or at least needs to be compiled for every emote. Maybe we can use QChar::isSpace there?