[datetime2] feat: new package with timezone-aware components

[vhellem]

edited by @adidahiya

Checklist

• Includes tests
• Update documentation

Changes proposed in this pull request:

• Create a new package @blueprintjs/datetime, which includes two new components:
  • DateInput2 (replacement for DateInput from @blueprintjs/datetime)
  • TimezoneSelect (replacement for TimezonePicker from @blueprintjs/timezone)
• Refer to new documentation for more info about these components and the package motivation

Reviewers should focus on:

• API for date input component

Not done in this PR

These new components are going to require a decent amount of iteration in real products before they are considered good from a UX/DX perspective and their APIs stable. As such, there are a number of improvements which we will not squeeze into this initial PR but leave for future PRs. These include:

1. comparison of date-fns library with alternatives like Luxon or the temporal-polyfill (see Moment.js project status post)
2. performance bottleneck with formatInTimeZone (https://github.com/marnusw/date-fns-tz#formatintimezone)
3. a smooth migration API from <DateInput>, which currently accepts a value: Date
   • there's a clear migration API we can provide here on the new <DateInput2> where we accept a Date or an ISO string, it will just require a bit more code
   • we should probably set hideTimezoneSelect: true by default
   • I'm confident that we can do it, and it's important that we do this so that consumers can quickly move over to the new component which uses Popover2, if they want to prioritize that migration over the timezone-awareness improvements in the new package
4. adding DateInput to the no-deprecated-components rule to encourage migration -- this should be done after the item 4 is addressed

Screenshot

[blueprint-bot]

bump CI cache key, add missing dependency to new package

Previews: documentation | landing | table | demo

[adidahiya]

The new timezone picker has much worse performance than the old one:

TimezonePicker	TimezonePickerV2

we'll need to dig into this with browser performance profiling...

[vhellem]

Done a number of improvements. Main drawback was probably that we rendered all items initially vs just a subset list, which I've added. Also done a lot more preprocessing.

[blueprint-bot]

Merge remote-tracking branch 'origin/develop' into vh/timezone-aware-date-input

Previews: documentation | landing | table | demo

[blueprint-bot]

Merge remote-tracking branch 'origin/develop' into vh/timezone-aware-date-input

Previews: documentation | landing | table | demo

most of my review comments have been addressed, and I will pick up the rest of the fixes to push this through. Thanks @vhellem!

[blueprint-bot]

fix lint

Previews: documentation | landing | table | demo

[blueprint-bot]

fix example width, add fill prop

Previews: documentation | landing | table | demo

[blueprint-bot]

Fix file names, improve docs

Previews: documentation | landing | table | demo

[blueprint-bot]

fix test and lint

Previews: documentation | landing | table | demo

[blueprint-bot]

TimezonePicker2 -> TimezoneSelect

Previews: documentation | landing | table | demo

[blueprint-bot]

run new package tests in CI

Previews: documentation | landing | table | demo

[blueprint-bot]

fix test suite

Previews: documentation | landing | table | demo

[blueprint-bot]

renames/refactors for code style; apply strict null checks

Previews: documentation | landing | table | demo

[blueprint-bot]

Fix version dep

Previews: documentation | landing | table | demo