[web] Add function (and an 'enum') for creating unique device ID on web

Summary:
Add a function and an auxiliary 'enum' (created via Object.freeze) for creating unique
device ID in javascript/flow.
Linear issue: https://linear.app/comm/issue/ENG-1279/initialize-deviceid-on-clients

Test Plan: Run provided tests.

Reviewers: tomek, max

Reviewed By: tomek, max

Subscribers: ashoat, adrian, atul, abosh

Differential Revision: https://phab.comm.dev/D4587