Fix Qt6 building

[pajlada]

Pull request checklist:

• CHANGELOG.md was updated, if applicable

Description

• Add Qt Core5Compat dependency if building with Qt6
• Add specialization to localizeNumber that accepts a qsizetype
• Add missing QFile include to SoundController.cpp
• Add missing QFile include to SettingsDialog.cpp
• Add missing QFile include to AboutPage.cpp
• Format IRC username-randomizer in IrcServer using QString arg
• Comment out usage of setCodec in LinkParser.cpp for Qt6
• Comment out usage of setCodec in AboutPage.cpp for Qt6
• Store max spaces as a qsizetype in CommandController
• Use QStringView.split instead of QString splitRef
• intify some usages of size
• Replace QStringRef with QStringView in TwitchMessageBuilder
• Replace QStringRef with QStringView in ResizingTextEdit
• Clarify QPoint constructor in SplitInput.cpp
• Use initFrom instead of init in QStyleOption
• Call result on QConcurrent runs in ModerationPage
• Add github workflow for building on Qt6

[github-actions]

clang-tidy made some suggestions

[Nerixyz]

This PR should also remove the following line:

chatterino2/src/PrecompiledHeader.hpp

Line 108 in d3499e8

# include <QtWidgets/QAction>

This header moved to QtGui but it's included above either way:

chatterino2/src/PrecompiledHeader.hpp

Line 16 in d3499e8

# include <QAction>

So it can be removed. CI doesn't catch this, since the Qt 6 runner has PCH disabled.