Suppress CS8305 for the generated Windows projections

The generated projection sources surface evaluation-only ([Experimental])
Windows Runtime APIs (e.g. Windows.Storage.Provider.StorageProviderShareLinkState,
Windows.ApplicationModel.DataTransfer.TransferTarget), which produce CS8305 and
fail under the projections' warnings-as-errors. These APIs are expected in a full
SDK projection, so add a NoWarn for CS8305 in the shared Projections
Directory.Build.props.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: Sergio0694

src/Projections/Directory.Build.props

@@ -19,6 +19,9 @@
     -->
     <WarningsNotAsErrors>$(WarningsNotAsErrors);CS0108;CS0109;CS0114;CS0219;CS0628;CS0660;CA2257</WarningsNotAsErrors>
 
+    <!-- Generated projections surface evaluation-only ([Experimental]) Windows Runtime APIs, so CS8305 is expected -->
+    <NoWarn>$(NoWarn);CS8305</NoWarn>
+
     <!-- Projections should not require runtime marshalling. -->
     <DisableRuntimeMarshalling>True</DisableRuntimeMarshalling>
     <CsWinRTAotOptimizerEnabled Condition="$([MSBuild]::GetTargetFrameworkVersion('$(TargetFramework)')) >= 6">Auto</CsWinRTAotOptimizerEnabled>