Update faust2caqt for QT6

[olilarkin]

Without this change faust2caqt fails due to the usage of std::filesystem in QT6, with errors such as:

    { return QtPrivate::toFilesystemPath(absoluteFilePath()); }

if supporting macOS < 10.15 is important, then this might not be the best fix

[olilarkin]

Actually, this is not enough.

QT6 has a dependency on librotli it seems and it's not in /usr/local/lib where the .app expects it.

It's possible to fix with

brew install librotli
sudo ln -s /opt/homebrew/lib/libbrotlicommon.1.dylib /usr/local/lib/

but that means the .app is not portable