[DatePicker/TimePicker] - Picker Keyboard Accessibility

[mlaursen]

The date picker is pretty terrible for keyboard users right now. After playing around with keyboard-only navigation for a bit, I think it should probably behave something like this.

All Pickers

• tab focus the picker
• spacebar to open the picker

Date Picker

• today, the defaultValue, or the value date is currently tab focused
• different dates can be selected by navigating with up, down, left, and right arrow keys
• pressing left on the first date or up on the first week will navigate to the previous month
• pressing right on the last date or down on the last week will navigate to the next month
• pressing space will select the date, but not confirm
• pressing enter will select the date and confirm/close the dialog
• tab will only allow focus on year picker toggle, month picker toggle, left/right arrow buttons, current selected date, cancel button, and ok button.

Year Picker

• current year or the defaultValue/value year will be currently focused
• years can be chosen by pressing up, down, left, or right (left simulates up, right simulates down)
• pressing space will select the year, but not confirm
• pressing enter will select the year and confirm/close the dialog
• tab will only allow focus on year picker toggle, month picker toggle, current active year, cancel button, and ok button.

Time Picker

• current hour or minute is focused
• can select hours/minutes by navigating with up, down, left, or right arrow keys
• can type the time with numbers. (06 -> selects 6, 6 -> selects 6, 5 - selects 5, 53 -> selects 53 (minutes), 3 (hours))
• tab will only allow focus on the clock face, the hour picker toggle, the minute picker toggle, am/pm, cancel button, and ok button.

Related: #193