Export all `utils` types

[MajorLift]

snaps repos have continued to expand its usage of utils types in the superstruct package.

Unfortunately, the workaround of importing from superstruct/dist/utils is no longer available in the @metamask/superstruct fork, so importing a new utils type will require a new version release going forward.

To avoid blocking downstream development, we should export all of the types in the utils submodule.