Remove `@types/jest`, and use Jest's own type annotations instead

[andiflabs]

Summary

This removes @types/jest in favor of @jest/types and friends. This allows using jest and expect to their full potential, and allow using new features like this: https://github.com/iron-fish/ironfish/blob/d8dffe54b17a3555efb013230726c3bb19eef784/ironfish/src/testUtilities/matchers/transaction.ts.

@types/jest was probably added at a time when Jest did not have any type annotations, but now that jest does have the annotations, it makes sense (in my opinion) to switch to using those. Some drawbacks:

• jest requires more verbose type annotations
• jest does not declare any global objects, so we have to do it by ourselves
• jest's types are more strict, and slightly incorrect code that used to compile before no longer compiles (this is not necessarily a drawback, but it's the reason why the delta is so large)

In addition to removing @types/jest, this PR also:

• removes some unused test functions
• changes incorrect uses of mockResolvedValue(Promise.resolved(x)) with mockResolvedValue(x)
• changes incorrect uses of toMatchObject(x) with toEqual(x)

Testing Plan

• yarn test

Documentation

N/A

Breaking Change

N/A