SI-8871 Fix specialization under REPL / FSC

The transformation of applications to specialized methods
relies on the owner of said method having had the specialization
info transform run which stashes a bunch of related data into
per-run caches such as `SpecializeTypes#{typeEnv}`.

Recently, we found that per-run caches didn't quite live up
to there name, and in fact weren't being cleaned up before
a new run. This was remedied in 00e11ff.

However, no good deed goes unpunished, and this led to a
regression in specialization in the REPL and FSC.

This commit makes two changes:

  - change the specialization info tranformer to no longer
    directly enter specialized methods into the `info` of whatever
    the current phase happens to be. This stops them showing up
    `enteringTyper` of the following run.
  - change `adaptInfos` to simply discard all but the oldest
    entry in the type history when bringing a symbol from one
    run into the next. This generalizes the approach taken to
    fix SI-7801. The specialization info transformer will now
    execute in each run, and repopulate `typeEnv` and friends.

I see that we have a seemingly related bandaid for this sort
of problem since 08505bd4ec. In a followup, I'll try to revert
that.
SI-5583 Remove the workaround for specialization bug

08505bd added a workaround for an undiagnosed interaction
between resident compilation and specialzation. This is no
longer needed after the previous commit.
SI-6613 Make Java enums work in FSC / REPL

We needed to hop from the enum's owner to its companion
module in an early phase of the compiler.

The enclosed test used to fail when this lookup returned
NoSymbol on the second run of the resident compiler when
triggered from `MixinTransformer`: the lookup didn't work
after the flatten info transform. This is related to the
fact that module classes are flattened into the enclosing
package, but module accessors remain in the enclosing class.
Merge pull request #4040 from retronym/ticket/8871

FSC / REPL Bug Bonanza