v0.18.4

Added GetIndex() and GetContext() to v3 low models.

Makes it much easier for downstream tools to know all the things

fix: indexing of operations which are $refs (#339)

Why
We have a linting rule which checks for duplicate operation IDs / duplicate operations. This linting rule wasn't catching duplicates if the operations were living in an external $ref.

What
Currently when building the index of operations we weren't checking for refs, this PR changes that.

@mfbx9da4