webchannel/cflags.go: Add Qt6WebChannelQuick to the pkg-config

[rcalixte]

This should aid the resolution for QQmlWebChannel

This should mean that this class can be moved back into the parent directory and the code can be removed, hopefully simplifying long-term maintenance.

[mappu]

I think this is related to the Qt version - it's not in Qt 6.4 in Debian Bookworm but it is present in Qt 6.8 in Debian Trixie.

I don't know exactly when the split happened, nor whether this is just a Debian thing or an upstream Qt thing. But I guess in order to support a broad range of Qt 6 versions, we're forced to split up the packages manually.

[rcalixte]

I don't know exactly when the split happened, nor whether this is just a Debian thing or an upstream Qt thing. But I guess in order to support a broad range of Qt 6 versions, we're forced to split up the packages manually.

Could this wait until there's a 6.8 branch and go exclusively in that branch? I don't see any Debian-specific patches for this (and it's an issue on Arch too) so I assume it was done upstream.