Modify TypeTransformers to give better diagnostics

[theunrepentantgeek]

Describe the current behavior

I've observed CoPilot getting stuck in a cycle trying to work out which type name to specify so that a TypeTransformer does the expected thing.

The root of the problem is that we rename types after the TypeTransformers run, so the final runtime type name isn't the right one.

Describe the improvement

We should detect when a TypeTransformer isn't used, and generate a useful error that can be used to correct the configuration. Our existing TypoAdvisor will be helpful here.