[datetime] fix(DateInput): don't close when clicking time arrows

[jez321]

Fixes #3474

Checklist

• Includes tests
• Update documentation

Changes proposed in this pull request:

• Set tabIndex=-1 on the timepicker arrow span element to ensure e.relatedTarget on the FocusEvent passed to handlePopoverBlur in dateInput is valid, preventing inappropriate closing of the popover.

Added tests and checked in latest Chrome, Firefox and Safari.

Reviewers should focus on:

• Whether the referenced bug has been fixed
• Whether setting tabIndex=-1 has any other side effects

Screenshot

Before	After

[palantirtech]

Thanks for your interest in palantir/blueprint, @jez321! Before we can accept your pull request, you need to sign our contributor license agreement - just visit https://cla.palantir.com/ and follow the instructions. Once you sign, I'll automatically update this pull request.

[jez321]

After doing a bit more thinking I think it might be better to find a way to fix this that doesn't require as a big a change as changing the timepicker arrows from a span to button so I'll play around a bit more and see if I can come up with something.

[jez321]

I've reverted the element type change and simply set tabIndex=-1 on the timepicker arrow span to ensure a valid relatedTarget is passed to focus events (specifically the FocusEvent passed to handlePopoverBlur in dateInput) which appears to fix the issue. Please let me know if this is acceptable or if you would like any changes to be made.

[adidahiya]

great, thanks!

[adidahiya]

PR preview docs build

it's a little hard to test in the docs site. we should probably add this option to show time picker arrows on all the date input components, similar to DatePicker:

[IzaGz]

I still have the problem on latest versions! ((( please help!