Flatpickr: Add id to altInput so a label can be added for it

[pimskie]

When using the altInput option, an alternative field is added to display a human-readable date.

The alternative field doesn't have an id. By giving the altInput field an id, a label can be associated with the altInput field. Now when the user clicks the label, the calendar opens.

[chmln]

Hello,

You don't need id and for to associate an input with a label.
Consider omitting those for calendar inputs.

I don't think this particular issue warrants extra code.
But thank you for contributing regardless :+1:

[timseverien]

I must ask you to reconsider, @chmln.

Association between label and input is important. Besides being super convenient for regular users (click label, go to field), it's imperative for a good screenreader experience.

There are a couple of ways to associate labels with inputs:

1. Wrap input in the label
2. Use the for-attribute

And there are a couple of ways to set a label on an input:

1. Using the title-attribute
2. Using the aria-label attribute

You don't need id and for to associate an input with a label.

With above statement, you seem to favor the former. That is fine. But with all respect, you can't expect everyone to follow your standards. There are valid use-cases for each of the above. Flatpickr currently doesn't provide any means to associate the altInput with a label, which is inconvenient for regular users and very confusing for users that depend on screenreaders. Don't neglect them.

With just 6 LOC, Flatpickr gets support for at least one strategy. Please do reconsider.

[danawoodman]

Bump. This is currently breaking our screen reader accessibility. Would be great to had support for passing in an HTML ID