Add a way for .superRefine() to narrow down the output type

[DanielBreiner]

Currently, refine has a type guard which is used to narrow down the output type.

refine<RefinedOutput extends Output>(
  check: (arg: Output) => arg is RefinedOutput,
  message?: /* ... */
): ZodEffects<this, RefinedOutput, RefinedOutput>;

superRefine: (
  refinement: RefinementEffect<Output>["refinement"]
) => ZodEffects<this, Output, Input>;

I propose adding this functionality to superRefine as well.

[maxArturo]

@DanielBreiner Agreed on this front. This is a fun little exercise in TS wrangling that I'm enjoying... :D

[maxArturo]

@DanielBreiner do you mind looking at #1615 and seeing if it works for you?

[DanielBreiner]

@maxArturo Looks great, thanks a lot for the PR.