Move nested type into its own file.

src/EditorFeatures/Core/EditorFeatures.csproj

@@ -113,6 +113,7 @@
     <Compile Include="Implementation\Intellisense\Completion\FilterResult.cs" />
     <Compile Include="Implementation\Structure\BlockTagState.cs" />
     <Compile Include="Implementation\Suggestions\SuggestedActionSetComparer.cs" />
+    <Compile Include="Implementation\Suggestions\SuggestedActionsSource.cs" />
     <Compile Include="Tags\ExportImageMonikerServiceAttribute.cs" />
     <Compile Include="Implementation\NavigateTo\AbstractNavigateToItemDisplay.cs" />
     <Compile Include="CommandArgs.cs" />