Specify AddRazorSupportForMvc in Blazor templates

VS 16.1 tooling does not support RazorConfigurations with no extensions
Working around this by treating Blazor templates as using MVC configuration
until we can resolve the issue in tooling

Workaround for https://github.com/aspnet/AspNetCore/issues/9119

src/Components/Blazor/Build/src/build/netstandard1.0/Microsoft.AspNetCore.Blazor.Build.props

@@ -1,3 +1,8 @@
 <Project>
   <Import Project="$(MSBuildThisFileDirectory)..\..\targets\All.props" />
-</Project>
+
+  <PropertyGroup>
+    <!-- Removing this tracked via https://github.com/aspnet/AspNetCore/issues/9126 -->
+    <AddRazorSupportForMvc>true</AddRazorSupportForMvc>
+  </PropertyGroup>
+</Project>

src/Components/Blazor/Templates/src/content/BlazorLibrary-CSharp/BlazorLibrary-CSharp.csproj

@@ -9,6 +9,7 @@
     </RestoreAdditionalProjectSources>
     <LangVersion>7.3</LangVersion>
     <RazorLangVersion>3.0</RazorLangVersion>
+    <AddRazorSupportForMvc>true</AddRazorSupportForMvc>
   </PropertyGroup>
 
   <ItemGroup>

src/ProjectTemplates/Web.ProjectTemplates/RazorClassLibrary-CSharp.csproj.in

@@ -6,7 +6,7 @@
     <RazorLangVersion Condition="'$(SupportPagesAndViews)' != 'True'">3.0</RazorLangVersion>
     <AddRazorSupportForMvc Condition="'$(SupportPagesAndViews)' == 'True'">true</AddRazorSupportForMvc>
     <RootNamespace Condition="'$(name)' != '$(name{-VALUE-FORMS-}safe_namespace)'">Company.RazorClassLibrary1</RootNamespace>
-    <AddRazorSupportForMvc Condition="'$(SupportPagesAndViews)' == 'True'">true</AddRazorSupportForMvc>
+    <AddRazorSupportForMvc>true</AddRazorSupportForMvc>
   </PropertyGroup>
 
   <ItemGroup Condition="'$(SupportPagesAndViews)' == 'True'">