[MR Widget V2] Undo dismiss should clear the dismissal feedback

Summary

Undoing a dismissed finding, then re-opening the modal for the same finding, shows the status as set back to Detected, but the dismissal card and comment are still shown:

Peek_2023-02-02_00-38

Implementation plan

• mr_security_reports_widget handles the revertDismiss logic. Update that to clear the dismissal_feedback of the finding object.

Verification plan

• Go to svedova/security-reports-v2!1
• Dismiss and undismiss a finding.
• After undismissed, reopening the modal should clear the dismissal comments