cleanup cached extension point class

GitOrigin-RevId: a726b3fbf85d099104d4c5ff79c85bc07b0fb042

platform/extensions/src/com/intellij/openapi/extensions/impl/ExtensionPointImpl.java

@@ -767,6 +767,10 @@ public abstract class ExtensionPointImpl<T> implements ExtensionPoint<T>, Iterab
     return extensionClass;
   }
 
+  public void clearExtensionClass() {
+    myExtensionClass = null;
+  }
+
   @Override
   public String toString() {
     return getName();