Re-implement lookaside for DFS during resolution

[dballance]

Description

cc @shockey - Lets try this again! 😆

In #1190 - the lookaside actually prevented traversal of all properties of a reference - because we marked it as traversed and checked for this traversal before fully iterating the properties in the patch. This means that DFS was never fully complete for a $ref that we marked as traversed. This moves the check for previous traversal out of the loop and allows a complete traversal but prevents future traversals. Should be accurate as far as I can tell.

I believe this was the root of "required" props not being parsed in swagger-api/swagger-ui#4000

Motivation and Context

Followup to #1201 and #1190. Again reduces resolution times to the #1190 range, but with greater accuracy.

How Has This Been Tested?

All tests pass. Tested with samples from swagger-api/swagger-editor#1585 & swagger-api/swagger-ui#4000 - doesn't appear to break those specs.

@shockey Unsure if there needs to be additional tests - so please grab and test as well! Might need to merge tests from #1201?

Types of changes

• No code changes (changes to documentation, CI, metadata, etc)
• Dependency changes (any modification to dependencies in package.json)
• 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:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.

[shockey]

Reviewing now - looks like my reversions did drop the tests from #1201, going to resolve that.

Edit: I must have been looking at this wrong locally 😄

[shockey]

Thanks @dballance! 😄