Include commit SHA in [AssemblyInformationalVersion] value (#22649)

* Add `[AssemblyMetadata("CommitHash", ...)]` to all C# assemblies
- see dotnet/arcade#5866 discussion
- provide the commit SHA though not in usual `[AssemblyInformationalVersion]` format

* Include `[AssemblyMetadata("Serviceable", "true")]` too
- see dotnet/arcade#1526

Directory.Build.targets

@@ -23,4 +23,21 @@
         PrivateAssets="all"
         IsImplicitlyDefined="true" />
   </ItemGroup>
+
+  <Target Name="GetCustomAssemblyAttributes"
+          BeforeTargets="GetAssemblyAttributes"
+          Condition=" '$(MSBuildProjectExtension)' == '.csproj' "
+          DependsOnTargets="InitializeSourceControlInformation">
+    <ItemGroup>
+      <AssemblyAttribute Include="System.Reflection.AssemblyMetadataAttribute" Condition="'$(SourceRevisionId)' != ''">
+        <_Parameter1>CommitHash</_Parameter1>
+        <_Parameter2>$(SourceRevisionId)</_Parameter2>
+      </AssemblyAttribute>
+
+      <AssemblyAttribute Include="System.Reflection.AssemblyMetadataAttribute" Condition="'$(Serviceable)' == 'true'">
+        <_Parameter1>Serviceable</_Parameter1>
+        <_Parameter2>True</_Parameter2>
+      </AssemblyAttribute>
+    </ItemGroup>
+  </Target>
 </Project>