Merge pull request #16338 from mattwire/note_timestamp

Convert civicrm_note.modified_date to timestamp

diff --cc CRM/Contribute/BAO/Contribution.php
Simple merge

diff --cc CRM/Contribute/Form/Contribution/Confirm.php
Simple merge

diff --cc CRM/Core/BAO/Note.php
Simple merge

diff --cc CRM/Event/BAO/Participant.php
Simple merge