Disable Workloads dependency on WiX nupkg during source-build to remove prebuilt

[dagood]

For #8014 (see issue for details/caveats)

After setting up the csproj, my process was to run a build with IncludeWiX=false, see which .cs files caused failures, change the extension to .wix.cs, and repeat. It seems to ended up pretty reasonably--at least, the files all seem to have to do with MSIs and not anything that could be useful for Linux. 😄

I'm running a 6.0 source-build with this change as a patch file to make sure it doesn't cause a downstream build error.

The intent is that this change doesn't affect "normal" builds at all.

[dagood]

This is seeming to work ok. (Removed the prebuilt in my tarball build, didn't cause runtime portable build to fail.) Submitted it as a 6.0.1xx patch here: dotnet/installer#12290 to burn down prebuilts until this dotnet/arcade PR flows.

[dagood]

@joeloff, @pjcollins, any problem with this approach?

The arcade-ci (Build Source-Build (Managed)) CI leg tests this change, so heads up that if you develop some new WiX MSI files, you might need to keep an eye on it and fix it. (You can test locally with source-build flags, or just setting /p:IncludeWiX=false.)

[dagood]

Closing: this PR stalled because there was no response, and it has a merge conflict now. The change is now carried in a patch file: https://github.com/dotnet/installer/blob/11ef768a808c6540426c83477c859326d0992f89/src/SourceBuild/tarball/patches/arcade/0009-Disable-Workloads-WiX-dependency-in-source-build.patch. I expect a new PR will be created in the future for a patch cleanup cycle. (And due to the nature of source-build, the patch conflict will have been resolved on the tail end of the build.)