[wasm][workload] Move emscripten to its own manifest for versioning reasons

[lewing]

Emsdk side dotnet/emsdk#29

[dotnet-issue-labeler]

I couldn't figure out the best area label to add to this PR. If you have write-permissions please help me learn by adding exactly one area label.

[joeloff]

I think this is fine, but we would need to stand up the same setup tasks we're planning for dotnet/runtime in dotnet/emsdk to produce installers and generate VS authoring

[lewing]

If it isn't required we don't need to do it but It sounds like we'll have the versioning problems otherwise?

[joeloff]

No, I think you're right. Let say EMSDK produces 6.0.0-preview7.123 and that flows to runtime. Runtime produces preview7.456 and we build MSIs for these and wrap them in nuget packages and push them.

But now runtime rebuilds for something else and produces 457. EMSDK hasn't changed, but we rebuild the closure to make sure everything is in sync for VS and CLI based installs. We'd end up trying to push the 123 package again which is already on the feed.

[lewing]

One thing that isn't clear to me here is should this name include the .Manifest-6.0.100 band or not? I assume so but I'm not sure what that implies about or later style band versioning

cc @dsplaisted

[dsplaisted]

No, the workload IDs in the workload manifest do not include band numbers. The NuGet packages that are created will.