Rename DiffusionSetPasswordPanel for consistency

Summary: Ref T5655.

Test Plan: arc lint and arc unit

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: Korvin, epriestley

Maniphest Tasks: T5655

Differential Revision: https://secure.phabricator.com/D11178