Summary:
Fixes some bugs involving intervals, and updates RandomizedTimer to support both fixed and
randomized delays, and to better handle async callbacks.
* Fixed a bug where Throttle would queue up many pidusage calls due to the use of
setInterval, and the async nature of the calls.
* Fixed a but where RandomizedTimer (now just Interval) would not be disabled in
ActiveDoc on doc shutdown if initialization had not yet settled.
Test Plan: Tested manually.
Reviewers: jarek, dsagal
Reviewed By: jarek, dsagal
Subscribers: dsagal
Differential Revision: https://phab.getgrist.com/D3604
