Intl.DateTimeFormat instances not cached slowing page load times

[deejay-hub]

Time Warp version
1.15

Describe the bug
DateTimeFormat constructors are being called repeatedly — once per record in getTimelineRecords, on every processTimeline call, inside the axis tick formatter (called per tick per redraw), and inside brushed (called continuously during drag). Each instantiation involves locale resolution which is non-trivial.