Allow project option to be visible to source generator

Author: Turnerj

Source/Directory.Build.props

@@ -7,6 +7,10 @@
     <SymbolPackageFormat>snupkg</SymbolPackageFormat>
   </PropertyGroup>
 
+  <ItemGroup Label="Source Generator Options">
+    <CompilerVisibleProperty Include="IncludePendingSchemaObjects" />
+  </ItemGroup>
+
   <PropertyGroup Label="Signing">
     <SignAssembly>true</SignAssembly>
     <AssemblyOriginatorKeyFile>../../Key.snk</AssemblyOriginatorKeyFile>