Add tests to verify linked modules work

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We're about to add support for linked modules.
First, however, we need to add test cases.

Essentially, we want to add tests for a couple cases and validate these work in the test, dev, and production environment:

• link to a package with newly introduced dependencies
• link to a package which specifies peer deps in our main project, barring installed dev dependencies (maybe covered by below case)
• Use required webpack loader only in cra project but missing from linked dep

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If possible, we want to also test that a:

• version of a dependency specified in the linked dependency is used over existing app (e.g. major version change with breaking incompatibility)

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#1912 and #1913