Remove requirements for VS 16.7

- use SignalR.Npm.FunctionalTests.npmproj to get non-stable version
  - not Microsoft.AspNetCore.DeveloperCertificates.XPlat.csproj (avoid C# and F# projects)
  - add `_GetPackageVersionInfo` target to all `*.npmproj` projects
    - make `_GetPackageVersionInfo` target work when `yarn` is not installed
- switch codesign-xplat.yml to use `dotnet msbuild`
  - above change also fixes Code-sign jobs but they're slightly faster using `dotnet msbuild`

.azure/pipelines/jobs/codesign-xplat.yml

@@ -31,6 +31,7 @@ jobs:
     - powershell: .\eng\common\build.ps1
         -ci
         -nobl
+        -msbuildEngine dotnet
         -restore
         -sign
         -publish

eng/Publishing.props

@@ -31,12 +31,14 @@
   </ItemGroup>
 
   <Target Name="_PublishInstallersAndChecksums">
-    <!-- 
-      This target is defined in eng/targets/Packaging.targets and included in every C# and F# project.
-      We use Microsoft.AspNetCore.DeveloperCertificates.XPlat because it is a nonshipping package, and we need a non-stable version string to use as our publish location.
-      If Microsoft.AspNetCore.DeveloperCertificates.XPlat ever becomes a shipping package, this logic will break, so be careful
+    <!--
+      This target is defined in eng/targets/Packaging.targets and Npm.Common.targets and included in every C#, F#,
+      and npm project. We use SignalR.Npm.FunctionalTests.npmproj because it is non-shipping (we need a non-stable
+      version string to use as our publish location), non-packed (won't be shipped in the future), and it is _not_ a
+      C# or F# project. For now at least, C# and F# projects should not be referenced when using desktop msbuild.
     -->
-    <MSBuild Projects="$(RepoRoot)src\Tools\FirstRunCertGenerator\src\Microsoft.AspNetCore.DeveloperCertificates.XPlat.csproj"
+    <MSBuild Projects="$(RepoRoot)src\SignalR\clients\ts\FunctionalTests\SignalR.Npm.FunctionalTests.npmproj"
+        Properties="DisableYarnCheck=true"
         Targets="_GetPackageVersionInfo"
         SkipNonexistentProjects="false">
       <Output TaskParameter="TargetOutputs" ItemName="_ResolvedPackageVersionInfo" />

eng/targets/Npm.Common.targets

@@ -29,7 +29,7 @@
     <BuildOutputFiles Include="dist\**\*.js" />
   </ItemGroup>
 
-  <Target Name="_CheckForInvalidConfiguration">
+  <Target Name="_CheckForInvalidConfiguration" Condition=" '$(DisableYarnCheck)' != 'true' ">
     <Error Text="Missing expected property: PackageId" Condition="'$(IsPackable)' != 'false' and '$(PackageId)' == ''" />
 
     <Exec ContinueOnError="true" Command="node -v" StandardOutputImportance="Low">
@@ -115,6 +115,19 @@
 
   <Target Name="Pack" Condition="'$(IsPackable)' == 'true'" DependsOnTargets="$(PackDependsOn)" />
 
+  <!-- This target is used to get the package versions of projects. A variant also exists in Packaging.targets. -->
+  <Target Name="_GetPackageVersionInfo" Returns="@(_ProjectPathWithVersion)">
+    <ItemGroup>
+      <_ProjectPathWithVersion Include="$(MSBuildProjectFullPath)">
+        <PackageId>$(PackageId)</PackageId>
+        <PackageVersion>$(PackageVersionForPackageVersionInfo)</PackageVersion>
+        <VersionSuffix>$(VersionSuffix)</VersionSuffix>
+        <!-- Fill in the item though variable names like "@microsoft/signalrPackageVersion" are likely invalid. -->
+        <VersionVariableName>$(PackageId.Replace('.',''))PackageVersion</VersionVariableName>
+      </_ProjectPathWithVersion>
+    </ItemGroup>
+  </Target>
+
   <Target Name="_RestoreBackupPackageJsonFile">
     <Move SourceFiles="$(_BackupPackageJson)" DestinationFiles="$(PackageJson)" />
   </Target>

eng/targets/Packaging.targets

@@ -7,7 +7,7 @@
                  See $(RepoRoot)eng\tools\BaselineGenerator\README.md for instructions on updating this baseline." />
   </Target>
 
-  <!-- This target is used to get the package versions of projects -->
+  <!-- This target is used to get the package versions of projects. A variant also exists in Npm.Common.targets. -->
   <Target Name="_GetPackageVersionInfo" DependsOnTargets="$(GetPackageVersionDependsOn)"
           Returns="@(_ProjectPathWithVersion)">
     <ItemGroup>