[master] Update dependencies from dotnet/arcade (#574)

[master] Update dependencies from dotnet/arcade
- Updates:
  - Microsoft.DotNet.Arcade.Sdk: from 5.0.0-beta.20117.3 to 5.0.0-beta.20374.1

 - Upadte xcopy-msbuild

 - Switch to Arcade UnitTest targets and props

 - Install the 3.1.0 runtime for test running

 - Use default test versions from Arcade

 - Work around implicit package reference warning

 - Set DOTNET_ROOT variable

 - Remove not working workaround for implicit package reference

 - Reference the XUnit Assert package

 - Lock to prior version of Microsoft.NET.Test.Sdk

Support for netcoreapp1.1 was removed in microsoft/vstest#2067 and
microsoft/vstest#2192, so we can no longer take updates to this package.

.vsts-pr.yaml

@@ -1,3 +1,7 @@
+variables:
+  - name: DOTNET_ROOT
+    value: $(Build.SourcesDirectory)\.dotnet
+
 jobs:
 - job: Windows
   pool:
@@ -44,7 +48,7 @@ jobs:
     - task: PublishTestResults@2
       inputs:
         testRunner: 'xUnit'
-        testResultsFiles: '**/*.xml' 
+        testResultsFiles: '**/*.xml'
         searchFolder: '$(Build.SourcesDirectory)\artifacts\TestResults\$(_configuration)'
         configuration: '$(_configuration)'
         publishRunAttachments: true

eng/Version.Details.xml

@@ -3,9 +3,9 @@
   <ProductDependencies>
   </ProductDependencies>
   <ToolsetDependencies>
-    <Dependency Name="Microsoft.DotNet.Arcade.Sdk" Version="5.0.0-beta.20117.3">
+    <Dependency Name="Microsoft.DotNet.Arcade.Sdk" Version="5.0.0-beta.20374.1">
       <Uri>https://github.com/dotnet/arcade</Uri>
-      <Sha>bd2a2b09716ddb54cb1e40f087beaaeeef859118</Sha>
+      <Sha>f6192d1e284a08ac05041d05fa6e60dec74b24f5</Sha>
     </Dependency>
   </ToolsetDependencies>
 </Dependencies>

eng/Versions.props

@@ -11,6 +11,10 @@
     <UsingToolMicrosoftNetCompilers>true</UsingToolMicrosoftNetCompilers>
     <UsingToolSymbolUploader>true</UsingToolSymbolUploader>
     <MicrosoftNetCompilersToolsetVersion>3.7.0-4.20351.2</MicrosoftNetCompilersToolsetVersion>
+
+    <!-- Force prior version due to https://github.com/microsoft/vstest/pull/2192 and https://github.com/microsoft/vstest/pull/2067 -->
+    <MicrosoftNETTestSdkVersion>16.1.1</MicrosoftNETTestSdkVersion>
+
     <!-- Dependencies -->
     <!-- Roslyn for VS 2019 -->
     <!-- NOTE: Do not upgrade these to be newer than what shipped in VS 2019 since the Syntax Visualizer extension still