Tests: Refactor test/unit/lib/plugins/aws/package/compile/events/stream.test.js

Most of the tests that currently cover core functionalities depend heavily on (and sometimes test) internal implementation characteristics. While they should be testing whether the given implementation produces desired outcome (treating its implementation more as a black box).

Current state of things is problematic for eventual internal improvements and refactors which occasionally we want to introduce, as in most of such cases proposed improvements need to be accompanied with counterproductive numerous updates to tests which are covering otherwise not altered functionalities .

At some point, we've introduced a new (black box based) way of testing the internals. It's through runServerless utility, which allows us to create a natural (as in real-world) serverless instance, and inspect the produced outcome for chosen command. More details here: https://github.com/serverless/serverless/tree/master/test#unit-tests

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This is issue is about refactoring test/unit/lib/plugins/aws/package/compile/events/stream.test.js to runServerless based variant.

It's needed, so we cleanly move forward with https://github.com/serverless/serverless/issues/8396

To make refactor relatively easy:

• Spec for new tests is fully defined and is already committed in. It's in the scope of this describe block: https://github.com/serverless/serverless/blob/654c50792ace1ee675fe5d6843faaafe1179bc25/test/unit/lib/plugins/aws/package/compile/events/stream.test.js#L1446-L1914
• Each test slot indicates which test it is about to replace
• It is indicated where (and how many) exactly runServerless runs are expected to happen, against which fixture and command they should be based
• Necessary hints are provided

For every refactored test, the old test should be removed

Refactor can be submitted with one PR, but partial refactors are also very welcome