Implement methods in newly created type from an inherited sealed class.

[rgrunber]

• When a non-existent type is permitted by a sealed class, the newly created type should implement the necessary methods
• Related #1553

.. turns out it's possible after all. Still need to clean it up a bit though.

[fbricon]

Creates a new class as you type 😂

[fbricon]

... and the generated classes don't even implement the interface method :-)

[rgrunber]

:joy: thanks for verifying in IDE. I think what's happening is the main issue I had from before. The creation of the problem marker, causes the associated text edit to also be created. In our case, the text edit immediately creates the type. I'll see what I can do.