[web] Prevent setting thread titles to multi-line strings

Summary: Web equivalent of D862. These aren't used a lot, but I figured it was better to keep them updated.

Test Plan: Flow

Reviewers: atul, karol-bisztyga, palys-swm

Subscribers: KatPo, zrebcu411, Adrian, subnub

Differential Revision: https://phabricator.ashoat.com/D863