`externalReferenceResolution` in `DereferenceOptions` doesn't work

[dslovinsky]

Expected behavior:

When set to "relative", relative paths should resolve relative to the directory. So this ref:
$ref: "./_shared/components.yaml#/components/schemas/uint256"
should resolve to:
<the directory the JSON schema is in>/_shared/components.yaml#/components/schemas/uint256

Actual behavior:

It always resolves against the CWD regardless of option choice.
So the above will get resolved as:
<root dir>/_shared/components.yaml#/components/schemas/uint256