PDF Control Panel methods for finding rems with the same PDF source

I posted this Feature Request to RemNote:

https://feedback.remnote.com/p/expose-sdk-method-to-query-all-rems-that-use-a-specific-rem-as-a-source-remshavingthisassource

Start with the linked RemNote feature request and inspect the plugin's PDF Control Panel integration. No repository file, test, or entry point is named, so first identify where these methods are implemented and confirm the SDK capability. Done means the requested way to find rems sharing a PDF source is available and verified.

Written by the indexing model from the issue text.