Build ProjectTemplates in Source-Build (#40643)

* Build ProjectTemplates in Source-Build

* Fixup

Directory.Build.props

@@ -31,6 +31,9 @@
           $(MSBuildProjectName.EndsWith('.FunctionalTest')) ) ">true</IsUnitTestProject>
     <IsUnitTestProject Condition=" '$(IsUnitTestProject)' == '' ">false</IsUnitTestProject>
     <IsTestAssetProject Condition=" $(RepoRelativeProjectDir.Contains('testassets')) OR $(MSBuildProjectName.Contains('TestCommon'))">true</IsTestAssetProject>
+    <IsProjectTemplateProject Condition=" ($(RepoRelativeProjectDir.Contains('ProjectTemplates')) OR $(MSBuildProjectName.Contains('ProjectTemplates')) ) AND
+        '$(IsUnitTestProject)' != 'true' AND
+        '$(IsTestAssetProject)' != 'true' ">true</IsProjectTemplateProject>
     <IsSampleProject Condition=" $(RepoRelativeProjectDir.ToUpperInvariant().Contains('SAMPLE')) ">true</IsSampleProject>
     <IsAnalyzersProject Condition="$(MSBuildProjectName.EndsWith('.Analyzers'))">true</IsAnalyzersProject>
     <IsShipping Condition=" '$(IsSampleProject)' == 'true' OR

Directory.Build.targets

 <Project>
   <PropertyGroup>
-    <!-- Only build Microsoft.AspNetCore.App, Microsoft.AspNetCore.App.Ref, and ref/ assemblies in source build. -->
+    <!-- Only build Microsoft.AspNetCore.App, Microsoft.AspNetCore.App.Ref, ref/ assemblies, and ProjectTemplates in source build. -->
     <!-- Analyzer package are needed in source build for WebSDK -->
     <ExcludeFromSourceBuild
-        Condition="'$(ExcludeFromSourceBuild)' == '' and '$(DotNetBuildFromSource)' == 'true' and '$(IsAspNetCoreApp)' != 'true' and '$(MSBuildProjectName)' != '$(TargetingPackName)' and '$(IsAnalyzersProject)' != 'true'">true</ExcludeFromSourceBuild>
+        Condition="'$(ExcludeFromSourceBuild)' == '' and 
+            '$(DotNetBuildFromSource)' == 'true' and 
+            '$(IsAspNetCoreApp)' != 'true' and 
+            '$(MSBuildProjectName)' != '$(TargetingPackName)' and 
+            '$(IsAnalyzersProject)' != 'true' and 
+            '$(IsProjectTemplateProject)' != 'true'">true</ExcludeFromSourceBuild>
 
     <!-- If the user has specified that they want to skip building any test related projects with SkipTestBuild,
      suppress all targets for TestProjects using ExcludeFromBuild. -->