Enable CS1591 errors for undocumented API

[ViktorHofer]

Similar as dotnet/extensions#4230, enable the CS1591 compiler errors when a library generates a documentation file.

[ViktorHofer]

@mconnew, @imcarolwang @HongGit can you please help fixing the build failures by documenting these APIs:

/__w/1/s/src/System.ServiceModel.Federation/src/System/ServiceModel/Federation/WSTrustChannelSecurityTokenProvider.cs(111,46): error CS1591: Missing XML comment for publicly visible type or member 'WSTrustChannelSecurityTokenProvider.ClientCredentials' [/__w/1/s/src/System.ServiceModel.Federation/src/System.ServiceModel.Federation.csproj]
/__w/1/s/src/System.ServiceModel.Federation/src/System/ServiceModel/Federation/WSTrustChannelSecurityTokenProvider.cs(439,30): error CS1591: Missing XML comment for publicly visible type or member 'WSTrustChannelSecurityTokenProvider.SupportsTokenCancellation' [/__w/1/s/src/System.ServiceModel.Federation/src/System.ServiceModel.Federation.csproj]
/__w/1/s/src/System.ServiceModel.Federation/src/System/ServiceModel/Federation/WSTrustChannelSecurityTokenProvider.cs(441,30): error CS1591: Missing XML comment for publicly visible type or member 'WSTrustChannelSecurityTokenProvider.SupportsTokenRenewal' [/__w/1/s/src/System.ServiceModel.Federation/src/System.ServiceModel.Federation.csproj]
/__w/1/s/src/System.ServiceModel.Federation/src/System/ServiceModel/Federation/WsTrustTokenParameters.cs(24,37): error CS1591: Missing XML comment for publicly visible type or member 'WSTrustTokenParameters.DefaultCacheIssuedTokens' [/__w/1/s/src/System.ServiceModel.Federation/src/System.ServiceModel.Federation.csproj]
/__w/1/s/src/System.ServiceModel.Federation/src/System/ServiceModel/Federation/WsTrustTokenParameters.cs(25,36): error CS1591: Missing XML comment for publicly visible type or member 'WSTrustTokenParameters.DefaultIssuedTokenRenewalThresholdPercentage' [/__w/1/s/src/System.ServiceModel.Federation/src/System.ServiceModel.Federation.csproj]
/__w/1/s/src/System.ServiceModel.Federation/src/System/ServiceModel/Federation/WsTrustTokenParameters.cs(26,41): error CS1591: Missing XML comment for publicly visible type or member 'WSTrustTokenParameters.DefaultMaxIssuedTokenCachingTime' [/__w/1/s/src/System.ServiceModel.Federation/src/System.ServiceModel.Federation.csproj]
/__w/1/s/src/System.ServiceModel.Federation/src/System/ServiceModel/Federation/WsTrustTokenParameters.cs(27,48): error CS1591: Missing XML comment for publicly visible type or member 'WSTrustTokenParameters.DefaultSecurityKeyType' [/__w/1/s/src/System.ServiceModel.Federation/src/System.ServiceModel.Federation.csproj]
/__w/1/s/src/System.ServiceModel.Federation/src/System/ServiceModel/Federation/WsTrustTokenParameters.cs(160,46): error CS1591: Missing XML comment for publicly visible type or member 'WSTrustTokenParameters.CreateWSFederationTokenParameters(Binding, EndpointAddress)' [/__w/1/s/src/System.ServiceModel.Federation/src/System.ServiceModel.Federation.csproj]
/__w/1/s/src/System.ServiceModel.Federation/src/System/ServiceModel/Federation/WsTrustTokenParameters.cs(172,46): error CS1591: Missing XML comment for publicly visible type or member 'WSTrustTokenParameters.CreateWS2007FederationTokenParameters(Binding, EndpointAddress)' [/__w/1/s/src/System.ServiceModel.Federation/src/System.ServiceModel.Federation.csproj]

[mconnew]

@StephenMolloy can you check the language of the documentation comment I've added.
@ViktorHofer, I also fixed the "build -vs" functionality in my update commit.

[StephenMolloy]

@StephenMolloy can you check the language of the documentation comment I've added.

Doc comments look fine to me.