title: How to create IEditorPart from IEditorDescriptor to use in MultiPageEditorPart?
body: <p>I have a class implementing IEditorPart as a page in my MultiPageEditorPart.
  Now I'd like to extend its functionality with ActionBarContributor and other Eclipse editor extensions.
  For that purpose, I've defined an extension for  org.eclipse.ui.editors, that points to my class. 
  This extension never get invoked as I create an instance of my class explicitly with new operator. Workbench allows creation of editors, but opens them in a new  editor window.</p>
  
  <p>How should an IEditorPart be created so that all extensions are applied to it and it can be used as MultiPageEditorPart.addPage() argument?</p>