<dynwind> no longer has "pre" or "post" fields

<dynwind> no longer has "pre" or "post" fields

* module/language/tree-il.scm (<tree-il>): Remove pre and post fields
  from <dynwind>.  A dynwind now assumes that in normal entry and exit,
  that the code runs the winders and unwinders using <seq> and
  <let-values> and such things.
  (parse-tree-il, unparse-tree-il, make-tree-il-folder, pre-post-order):
  Adapt <dynwind> users.

* module/language/tree-il/analyze.scm (analyze-lexicals):
* module/language/tree-il/compile-glil.scm (flatten-lambda-case):
* module/language/tree-il/cse.scm (cse):
* module/language/tree-il/debug.scm (verify-tree-il):
* module/language/tree-il/effects.scm (make-effects-analyzer): Adapt.

* module/language/tree-il/peval.scm (peval):
* module/language/tree-il/primitives.scm (*primitive-expand-table*):
  Produce tree-il that calls the winder and unwinder.  Recognize
  singly-valued dynamic-wind expressions.

* test-suite/tests/peval.test ("partial evaluation"): Add tests.