Support .NET 8 & latest C# lang features

[NotNite]

• This does not prevent someone setting target framework to net8.0 in their csproj. I guess I could inspect the assembly metadata for each .dll and check their framework, but that feels like overcomplicating it when I can just ask PAC to check a single line. Requesting opinions.
• Tested on this failed commit to Pet Nicknames: https://github.com/goatcorp/DalamudPluginsD17/pull/2977/commits/92db85d3ab30c32b8038ca4828dd1596efeaf72e which had latest C# language features in it.
  • I also tested the latest Better in Blue manifest, but someone probably wants to take the entire DP17 repo and build with this.

[NotNite]

With the .NET 8 release, plugins no longer build:

[12:02:26 INF] /work/repo/OfDungeonsDeep/OfDungeonsDeep.csproj : error NU1102: Unable to find package Microsoft.NETCore.App.Ref with version (= 7.0.17)
[12:02:26 INF] /work/repo/OfDungeonsDeep/OfDungeonsDeep.csproj : error NU1102:   - Found 1 version(s) in /packages [ Nearest version: 8.0.0 ]
[12:02:26 INF] /work/repo/OfDungeonsDeep/OfDungeonsDeep.csproj : error NU1102: Unable to find package Microsoft.AspNetCore.App.Ref with version (= 7.0.17)
[12:02:26 INF] /work/repo/OfDungeonsDeep/OfDungeonsDeep.csproj : error NU1102:   - Found 1 version(s) in /packages [ Nearest version: 8.0.0 ]
[12:02:26 INF]   Failed to restore /work/repo/OfDungeonsDeep/OfDungeonsDeep.csproj (in 1.59 sec).
[12:02:26 INF]
[12:02:26 INF] Build FAILED.

This can be fixed by fetching 7.0.17 in RUNTIME_PACKAGES, but I don't know why it's trying to fetch that one specifically.

[NotNite]

Turns out it's channel track overrides. When staging gets .NET 8, this should be fine to merge(?).