[#346] Add getStorage'

Description

Problem: We have an open issue (#346 (closed)) for adding proper support for storages with big_maps to cleveland. However, that will take a while to complete and, in the meantime, it would be nice to at least be able to do in emulator-only tests.

We do have checkStorage', but it's not versatile enough, and is not enough for a lot of use cases.

Solution: Add a getStorage' function that supports storages with big_maps only in emulator tests. This should be enough to do any kind of storage checks. When #346 (closed) is fully implemented, we can remove this function (and checkStorage' too).

Related issue(s)

Resolves part of #346 (closed)

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