This is a test

... and drop the old ElimByName.

I tried to extend specialization to all context functions, not just ones of 0 arity.
But that runs into problems for dependent context functions, since the necessary casts
get complicated. Since context functions over primitive types are an anti-pattern anyway
I don't think we need to optimize this case, after all.

 - Split out forward reference checks and cross version (i.e. experimental/deprecated) checks
   into their own miniphases. These have nothing to do with the core tasks of RefChecks.
 - Move RefChecks earlier in the pipeline, so that it is not affected by ElimByName's questionable
   type manipulations.

Perform the overriding checks after elimByName. I observed some problem with
catsEffect2, where a super accessor method with a `() ?=> T` parameter was compared with a
corresponding super accessor method with a `=> T` parameter. One of these methods was generated
before elimByName, the other after. So comparing them at phase elimRepeated + 1 gave two different
types. The problem is fixed by comparing after elimByName, which means that the type of the second
method is converted to match the first.