Remove Separator. It's not used anymore
Call getClass 30 times less in TreeTransforms initialisation.
Precompute initial NXTransformations in TreeTransforms.

Helps Annotation transformers which do not need to reinitialise themselves anymore.
Make TreeTransform type check in dotty. There's no magic type behind getClass in dotty.
Merge pull request #272 from dotty-staging/cache-nx-info

Precompute NXTransforms to speedup repeated application of TreeTransformer.macroTransform