1.0.8.25: refactor CAN-OPTIMIZE-ACCESS usage and interface

1.0.8.25: refactor CAN-OPTIMIZE-ACCESS usage and interface

* Make the constant slot-name and the possible new-value-form
  additional return values.

* Use CONSTANT-FORM-VALUE instead of EVAL to get the constant
  slot-name. Also use the environment correctly to CONSTANTP
  and CONSTANT-FORM-VALUE.

* Call CAN-OPTIMIZE-ACCESS in the various instance-access optimizers
  and not around calls to them, so that they can directly use the
  slot-name and new-value-form results from CAN-OPTIMIZE-ACCESS
  instead of having to recompute them.