Add net8.0-windows to WinAppSdk

[Arlodotexe]

This PR:

• Updates dotnet version to 8.0 (for CI, codespaces, etc)
• Updates the submodule to include net8.0-windows10.0.22621.0 as an available TFM under WinAppSdk.

Prerequisite PR: CommunityToolkit/Tooling-Windows-Submodule#165

[Arlodotexe]

Looks like our blocker was resolved by this commit, but some lingering issues still remain regarding package conflicts (see here).

[michael-hawker]

@Arlodotexe try updating slngen, we're on a version that's pretty old now:

Windows/.config/dotnet-tools.json

Lines 17 to 22 in f9ce94a

	"microsoft.visualstudio.slngen.tool": {
	"version": "9.5.4",
	"commands": [
	"slngen"
	]
	}

Latest is 11.2.3

[Arlodotexe]

Need to put together the Labs PR and make sure that's clear before we can merge the tooling PR.