Add string literal suffixes to create QStrings, QByteArrays, and QLatin1String(View)s at compile time

[Nerixyz]

Description

To create a string/byte-array at compile-time before this PR, you'd need to use Q{String, ByteArray}Literal. These macros would embed the generated data into the executable, so no allocation at runtime would be required. Qt 6.4 introduced the Qt::Literals::StringLiterals namespace, which provides suffixes to create the aforementioned types (and QLatin1Char). From the documentation of the QString suffix (applies to the others as well):

The QString is created at compile time, and the generated string data is stored in the read-only segment of the compiled object file. Duplicate literals may share the same read-only memory. This functionality is interchangeable with QStringLiteral, but saves typing when many string literals are present in the code.

The last point is the most important one in my opinion. To create a QString you can now do u"Chatterino"_s instead of QStringLiteral("Chatterino").

Since Chatterino also supports Qt 5, I ported the functionality using the implementation from desktop-app/lib_base which itself is based on the QStringLiteral macro from Qt 5. I added tests to ensure the implementation yields the same result.

The implementation for Qt 6 is a lot simpler thanks to refactored QString internals.

Ideally, most literals should use this suffix, since it reduces small, temporary allocations.