Improve tracing in Simplifier
Refactor buildClass and mkDictSelId a bit, to avoid the no_unf argument

No change in functionality, just a cleaner story, with the RHS for
dictionary selectors being treated less specially than before.
Mark evaluated arguments in dataConInstPat

See Note [Mark evaluated arguments] in CoreUtils.

This is not a significant change, but avoids a spurious Lint complaint.
Preserve evaluated-ness in CoreTidy

The main effect of this patch is to preserve the evaluated-ness of
case binders and suchlike, to avoid spurious Lint complaints after
tidying.  See Note [Preserve evaluatedness] in CoreTidy.

Plus a bit of associated refactoring of tidyIdBndr, tidyLetBndr.
Better error message in vectoriser
Error message wibble, presumably due to recent changes in transformers