Open windows do not refresh with other windows change

[sharwell]

Currently, refreshing the Inheritance Margin glyphs is only triggered by two things:

1. Opening a document (refreshes that document)
2. Typing in a document (when you stop, that document gets refreshed)

Notably missing from this list is the case where another document is updated which affects the current document. For example:

1. Open IMyType.cs containing the following interface:

   public interface IMyType
   {
     void Method(int argument);
   }

2. Open MyType.cs containing the following class:

   public class MyType
   {
     public void Method(int argument) { }
   }

3. Observe: In MyType.cs, the Method method has an inheritance glyph next to it.

4. In IMyType.cs, change the signature of Method to the following:

   void Method(short argument);

5. Observe: In IMyType.cs, the Method method no longer has an inheritance glyph next to it.

6. Observe: In MyType.cs, the Method method does have an inheritance glyph next to it, even though the method no longer implements any interface method.