Use SetMultipleModeledMethodsMessage in modeled methods panel

[koesie10]

This makes the modeled methods panel send the SetMultipleModeledMethodsMessage message when the modeled methods change. This is the last step in wiring up the modeled methods panel; after this has been merged, it is possible to view, edit and save multiple models in the method modeling panel.

The only remaining usage of convertToLegacyModeledMethod is in the ModeledMethodsPanel when the feature flag is disabled. In this case, we're using a different code path, but once the feature flag is removed, it should be possible to remove convertToLegacyModeledMethod.

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]

LGTM