[web] update calculateMaxTextWidth to consider different font sizes

Summary:
Our reaction tooltip has texts with two different font sizes (see image below for context) to accommodate for this I updated calculateMaxTextWidth to consider different font sizes so that we can use this function when we introduce the reaction tooltip

Depends on D8829

Test Plan: flow and confirmed that the result of calculateMaxTextWidth was the same before and after the changes

Reviewers: atul, kamil

Reviewed By: kamil

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D8831