Fix System.Private.ServiceModel.dll's Uapaot Build.

[shmao]

I made the following changes

1. Removed uapaot-Windows_NT from System.Private.ServiceModel/src/Configurations.props. We should be able to use the uap build for uapaot. We used to have netcore50 only.
2. Replaced netcore50 with uap in System.Private.ServiceModel.csproj
3. Added required references when targetgroup==uap.
4. Added a new package for the above required references.
5. Fixed some code that not worked with NS2.0.

Fix #2001
Fix #2002
Fix #2003
Fix #2005

[dagood]

I can't comment on the C# changes, but build changes LGTM.

[shmao]

@dagood Thanks for reviewing the PR. Do you have any ideas about the following error,

15:49:34 [xUnit] [INFO] - [xUnit.Net-v2 (default)] - No test report file(s) were found with the pattern 'bin/Windows_NT.AnyCPU.Debug//testResults.xml' relative to 'D:\j\workspace\windows_nt_de---f3649c3b' for the testing framework 'xUnit.Net-v2 (default)'. Did you enter a pattern relative to the correct directory? Did you generate the result report(s) for 'xUnit.Net-v2 (default)'?
15:49:34
[xUnit] [ERROR] - No test reports found for the metric 'xUnit.Net' with the resolved pattern 'bin/Windows_NT.AnyCPU.Debug//testResults.xml'. Configuration error?.

The tests passed. But testResults.xml couldn't be found.

[StephenBonikowsky]

Those are CI issues I'm working on, don't block your merge on it.

[StephenBonikowsky]

LGTM, although I'd like to know more about the code we stripped out, I can follow-up offline.

[StephenBonikowsky]

@dotnet-bot test ci please

[shmao]

@StephenBonikowsky The removed classes were added because they were not available on netcore50, so we make a internal copy of the framework type. As the types are available in NS2.0, we can remove them. Otherwise, the build would complain about ambiguous types.

[zhenlan]

Can we please remove this section? #2006

[mconnew]

@dotnet-bot test all outerloop please

[mconnew]

@dotnet-bot test all innerloop please

[zhenlan]

Thanks @shmao!