Switch ModeledMethod to union of types

[koesie10]

This switches the ModeledMethod type from 1 type containing all fields to a union of multiple types where each type accurately represents which fields are present for a specific model. This allows more disjointed models to be represented more accurately, such as type models. For type models, having input, output, etc. doesn't make sense. It instead has fields like type1, type2 and path. I don't think adding these properties to every modeled method makes sense, so this is a solution which allows us to represent both models.

This is a very large changeset, but I don't think splitting it up would be helpful (I don't really see how). A lot of the changes are changes to method names or removing unnecessary properties.

Checklist

• CHANGELOG.md has been updated to incorporate all user visible changes made by this pull request.
• Issues have been created for any UI or other user-facing changes made by this pull request.
• [Maintainers only] If this pull request makes user-facing changes that require documentation changes, open a corresponding docs pull request in the github/codeql repo and add the ready-for-doc-review label there.

[robertbrignull]

I think this looks really good! I like splitting the ModeledMethod type up so that each sub-type only contains the fields it needs.

I have a few small comments asking for clarification or small improvements, but the overall idea and changes look great.

[robertbrignull]

LGTM

(Has some conflicts in imports, but they didn't seem hard to fix)