## Motivation

`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
new `utils` types will require new version releases going forward.

To prevent this from blocking downstream development, this commit adds
all currently available types in the `utils` submodule as package-level
exports.

## Description

- Newly exports the following types: `Assign`, `If`, `IsUnion`,
`ObjectType`, `PartialObjectSchema`, `StructSchema`, `TupleSchema`

## References

- Closes #26
- Blocking MetaMask/snaps#2445
  - Blocking MetaMask/snaps#2514

- `create-release-pr` action is failing due to this issue:
MetaMask/action-create-release-pr#138
- Removing unreleased changelog entries should unblock this, enabling a
release candidate to be created.

This is the release candidate for version 3.1.0.

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Co-authored-by: github-actions <github-actions@github.com>
Co-authored-by: Jongsun Suh <jongsun.suh@icloud.com>