Add support for partial component class editing -> refresh components.

- We now do aggressive detection on the type of C# class that's being edited. In order to not impact C# scenarios we only do work if C# assets are available to us. Meaning, we inspect the old document and if that document has its' semantic model available we spend cycles to determine if it's a component. In the case that we find a C# component class that wasn't previously caught we enqueue an update.
- Added several tests to ensure we enqueue and that we properly detect component classes.

aspnet/AspNetCoredotnet/aspnetcore-tooling#14646
\n\nCommit migrated from d8b62e121f

src/Razor/Microsoft.CodeAnalysis.Razor/src/ComponentDetectionConventions.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;
+
+namespace Microsoft.CodeAnalysis.Razor
+{
+    internal static class ComponentDetectionConventions
+    {
+        public static bool IsComponent(INamedTypeSymbol symbol, INamedTypeSymbol icomponentSymbol)
+        {
+            if (symbol is null)
+            {
+                throw new ArgumentNullException(nameof(symbol));
+            }
+
+            if (icomponentSymbol is null)
+            {
+                throw new ArgumentNullException(nameof(icomponentSymbol));
+            }
+
+            return
+                symbol.DeclaredAccessibility == Accessibility.Public &&
+                !symbol.IsAbstract &&
+                symbol.AllInterfaces.Contains(icomponentSymbol);
+        }
+    }
+}

src/Razor/Microsoft.CodeAnalysis.Razor/src/ComponentTagHelperDescriptorProvider.cs

@@ -573,10 +573,8 @@ namespace Microsoft.CodeAnalysis.Razor
                     return false;
                 }
 
-                return
-                    symbol.DeclaredAccessibility == Accessibility.Public &&
-                    !symbol.IsAbstract &&
-                    symbol.AllInterfaces.Contains(_symbols.IComponent);
+                var isComponent = ComponentDetectionConventions.IsComponent(symbol, _symbols.IComponent);
+                return isComponent;
             }
         }
     }