Upgrade XIVLauncher.Core to net8

[Blooym]

No description provided.

[Maia-Everett]

Yes, please! .NET 6 has been removed from Ubuntu 24.04 LTS, which is releasing this week. I've already had to patch the csproj for building against .NET 8 for the PPA.

[KazWolfe]

Would this affect users on Ubuntu 20.04? While 22.04 and newer seem to have .NET 8 in their repos, 20.04 is still supported for another year and does not (although MS' documentation states that you'd need to add their apt repo anyways, so possibly a moot point).

[Maia-Everett]

Yes, Ubuntu 22.04 and later all have .NET 8 in the official repository, and earlier Ubuntu versions, including 20.04, don't have any version of .NET in the official repository and will have to add the Microsoft repository, which includes .NET 8.

https://learn.microsoft.com/en-us/dotnet/core/install/linux-ubuntu-install?pivots=os-linux-ubuntu-2004&tabs=dotnet8

[rankynbass]

This works just fine, and seems to be necessary to get XIVLauncher.Core to build inside a flatpak. However, XL.Common also needs to be updated to net8 for the flatpak build, and I'm not sure how that affects things on the Windows side.