[web] Add message timestamp to MessageActionButtons component

Summary:
Display message timestamp in MessageActionButtons on hover. Additional context here: https://linear.app/comm/issue/ENG-799/message-tooltip-position-is-incorrect

Depends on D3570

Test Plan:
Looks as expected:

Reviewers: def-au1t, palys-swm, ashoat, benschac

Reviewed By: ashoat

Subscribers: Adrian, karol-bisztyga, yayabosh

Differential Revision: https://phabricator.ashoat.com/D3571