Revert "Remove opt in for new schema for CombineTargetFrameworkInfoPr…

…operties (dotnet#6928)"

This caused a regression in scenarios using Visual Studio 17.3 previews
with `global.json` files pointing to old .NET SDKs.

This reverts commit fe4fde9.

Conflicts:
	src/Framework/ChangeWaves.cs
	src/Tasks/CombineTargetFrameworkInfoProperties.cs

src/Tasks/CombineTargetFrameworkInfoProperties.cs

@@ -39,8 +39,7 @@ public override bool Execute()
         {
             if (PropertiesAndValues != null)
             {
-                // When removing the change wave, also remove UseAttributeForTargetFrameworkInfoPropertyNames.
-                XElement root = ChangeWaves.AreFeaturesEnabled(ChangeWaves.Wave17_4) || UseAttributeForTargetFrameworkInfoPropertyNames ?
+                XElement root = UseAttributeForTargetFrameworkInfoPropertyNames ?
                     new("TargetFramework", new XAttribute("Name", EscapingUtilities.Escape(RootElementName))) :
                     new(RootElementName);
 

src/Tasks/Microsoft.Common.CurrentVersion.targets

@@ -1907,9 +1907,14 @@ Copyright (C) Microsoft Corporation. All rights reserved.
       </_AdditionalTargetFrameworkInfoPropertyWithValue>
     </ItemGroup>
 
+    <PropertyGroup>
+      <_UseAttributeForTargetFrameworkInfoPropertyNames Condition="'$(_UseAttributeForTargetFrameworkInfoPropertyNames)' == ''">false</_UseAttributeForTargetFrameworkInfoPropertyNames>
+    </PropertyGroup>
+
     <CombineTargetFrameworkInfoProperties
         RootElementName="$(TargetFramework)"
-        PropertiesAndValues="@(_AdditionalTargetFrameworkInfoPropertyWithValue)">
+        PropertiesAndValues="@(_AdditionalTargetFrameworkInfoPropertyWithValue)"
+        UseAttributeForTargetFrameworkInfoPropertyNames="$(_UseAttributeForTargetFrameworkInfoPropertyNames)">
       <Output TaskParameter="Result"
               PropertyName="_AdditionalTargetFrameworkInfoProperties"/>
     </CombineTargetFrameworkInfoProperties>