convert relative refs when resolving an external schema

[brendarearden]

Motivation and Context

stoplightio/prism#2385
This also seems to be related APIDevTools#200

Getting error MissingPointerError when $ref has a sibling of any type.

Description

Pulled the changes from: karlvr@6d2740b
Additionally I removed file:// from showing up in the relative path.
Added test helper to update the expected value

How Has This Been Tested?

Ran tests locally and all passed.
Tested manually in Prism by manually changing the node_module files
Ran Prism tests locally and all passed.

Screenshot(s)/recordings(s)

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• This PR's code follows as closely as possible the coding style/guidelines of this project.
• I have added error reporting and followed the error reporting guidelines.
• I have added event tracking and followed the event tracking guidelines.
• I have updated any relevant documentation accordingly to reflect this PR's changes.
• I have added automated tests (unit/integration/e2e/other) to cover my changes.
• All new and existing tests pass locally (excluding flaky CI tests).

[chohmann]

woohoo!