Extract createPendingSidebar function
Summary: createPendingSidebar will be used in other tooltips
Test Plan: Flow, make sure creating sidebars from text messages still works
Reviewers: ashoat, palys-swm
Reviewed By: ashoat
Subscribers: zrebcu411, Adrian, atul, subnub
Differential Revision: https://phabricator.ashoat.com/D601