Update Microsoft.Net.Sdk.WorkloadManifestReader to RTM version

[MattGal]

#7880 - there were a couple small breaking changes that required minor updates. This change passes all tests but it is possible further breaking changes may be found later.

To double check:

• The right tests are in and and the right validation has happened. Guidance: https://github.com/dotnet/core-eng/tree/master/Documentation/Validation

[riarenas]

I have no idea what any of these versions are or what this component is used for. The update seems fine though.

[MattGal]

I've verified via debugging w/ the tests that the changes give the results I'd expect; there is some expectation that this may no longer be in use since we'd expect this update to have already occurred if so, but we can address that in the future if we have to.

[joeloff]

If there were changes in the behavior it could impact the generated workload packs/manifests for VS. There's no way to tell until you actually do a full build of the workloads, e.g. EMSDK or runtime (for the mono workloads), but this should be okay