Use base postMessage instead of webview one

[charisk]

I noticed we were still using this.webviewView.webview.postMessage in a couple of places in the method modeling panel so I fixed that and by doing that a type mismatch was flagged and fixed.

Checklist

N/A:

• 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.