[web] Introduce toggleReplyTooltip and toggleSidebarTooltip

Summary:
Previously, an "alt text" tooltip would only appear for the sidebar button. This enables it for the reply button.

Before:

After:

(Styling, tooltip arrow, etc coming in future diffs)

Test Plan: Manual testing

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

Reviewed By: palys-swm, ashoat

Subscribers: ashoat, Adrian, karol-bisztyga

Differential Revision: https://phabricator.ashoat.com/D3355