Summary:
- With a format like "DD-MM-YYYY" or "DD MMM YYYY", allow parsing dates
with two digit year or numeric month (like "16-8-21").
- Interpret two-digit years in the same way for moment parsing and for
bootstrap-datepicker.
- For partial inputs (like "8/16"), when a format is present, assume that
provided parts cover the date, then month, then year (even for a format that
starts with year).
Test Plan: Expanded a unittest
Reviewers: alexmojaki
Reviewed By: alexmojaki
Subscribers: alexmojaki
Differential Revision: https://phab.getgrist.com/D2985