Add IDE extensibility for project engine

src/Microsoft.CodeAnalysis.Razor.Workspaces/ExportCustomProjectEngineFactoryAttribute.cs

@@ -0,0 +1,28 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System;
+using System.Composition;
+
+namespace Microsoft.CodeAnalysis.Razor
+{
+    [MetadataAttribute]
+    [AttributeUsage(AttributeTargets.Class, AllowMultiple = false, Inherited = true)]
+    public class ExportCustomProjectEngineFactoryAttribute : ExportAttribute, ICustomProjectEngineFactoryMetadata
+    {
+        public ExportCustomProjectEngineFactoryAttribute(string configurationName)
+            : base(typeof(IProjectEngineFactory))
+        {
+            if (configurationName == null)
+            {
+                throw new ArgumentNullException(nameof(configurationName));
+            }
+
+            ConfigurationName = configurationName;
+        }
+
+        public string ConfigurationName { get; }
+
+        public bool SupportsSerialization { get; set; }
+    }
+}

src/Microsoft.CodeAnalysis.Razor.Workspaces/ICustomProjectEngineFactoryMetadata.cs

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+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+namespace Microsoft.CodeAnalysis.Razor
+{
+    public interface ICustomProjectEngineFactoryMetadata
+    {
+        string ConfigurationName { get; }
+
+        bool SupportsSerialization { get; }
+    }
+}

src/Microsoft.CodeAnalysis.Razor.Workspaces/IProjectEngineFactory.cs

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+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System;
+using Microsoft.AspNetCore.Razor.Language;
+
+namespace Microsoft.CodeAnalysis.Razor
+{
+    public interface IProjectEngineFactory
+    {
+        RazorProjectEngine Create(RazorConfiguration configuration, RazorProjectFileSystem fileSystem, Action<RazorProjectEngineBuilder> configure);
+    }
+}