Intent to prototype and ship: Time picker UI

[Sam Johnson]

As of Firefox 154, I intend to turn on the time picker UI for <input type="time"> and <input type="datetime-local"> by default on all platforms. It has been developed behind the dom.forms.datetime.timepicker preference.

Summary:
Add a time picker UI for <input type="time"> and <input type="datetime-local">, which functions similarly to the existing date picker UI. This allows users to select a time using accessible, intuitive controls.

Bug to turn on by default:
https://bugzilla.mozilla.org/show_bug.cgi?id=1726107

Specification:
https://html.spec.whatwg.org/multipage/input.html#input-support-picker

Input picker support is implementation-defined, and noted as commonly available for time and datetime-local input types.

Standards Body:
WHATWG

Platform Coverage:
All

Preference:
dom.forms.datetime.timepicker

DevTools Bug:
N/A

Extensions Bug:
N/A

Use Counter:
N/A

Standards-Positions Discussion:
N/A

Other Browsers:
Blink: Shipped
WebKit: Shipped on mobile, not implemented on desktop

web-platform-tests:
The picker UI itself is not covered by web-platform-tests due to picker support being implementation-defined behavior. Web-exposed functionality is already covered by existing tests in html/semantics/forms/the-input-element which continue to pass with the time picker UI enabled.