Use the same logic for hiding methods in model editor and usages panel

[robertbrignull]

Makes sure that the model editor and the usages panel are using the same logic when deciding whether to show or hide a method.

Before this PR, you wouldn't be able to view usages of any methods that were already modeled and the modeling had been saved. We previously thought this bug only applied when you had modelings coming from an external pack, but you can reproduce it within one pack too.

Steps to reproduce:

• Add a modeling to a method
• Save the extension pack
• Click "View" on the modeled method and observe that nothing happens

With this PR, the usages panel and the model editor are fully in sync and show the same methods and clicking "View" always highlights the method in the usages panel.

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.

[charisk]

LGTM!