Produce Windows PDBs when building for netfx and in a Windows OS (#28562)

* Produce Windows PDBs when building for netfx and in a Windows OS

* Use TargetGroup and RunningOnUnix instead

Author: safern

dir.props

@@ -174,6 +174,8 @@
   <!-- Set the kind of PDB to Portable and turn on SourceLink (fetching source from GitHub) -->
   <PropertyGroup>
     <DebugType Condition="'$(DebugType)' == ''">Portable</DebugType>
+    <!-- Empty DebugType when building for netfx and in windows so that it is set to full or pdbonly later -->
+    <DebugType Condition="'$(TargetsNetFx)' == 'true' AND '$(RunningOnUnix)' != 'true'"></DebugType>
     <UseSourceLink>true</UseSourceLink>
   </PropertyGroup>