Implement format for datetime

[oandregal]

Closes #73154
Depends on #73922

What?

Implements format for datetime.

Why?

It's the last of the formats we need to implement from #73154

How?

• Adds a format with datetime and weekStartsOn props.

Testing Instructions

Visit the datetime field type storybook:

Screen.Recording.2025-12-11.at.19.03.12.mov

[oandregal]

#73922 needs to land first. I'll rebase and add the changelog when that's done.

[oandregal]

There's an extra space between the hour and the minutes coming from this default:

[oandregal]

The default is defined here:

formats: {
		time: 'g: i a',
		date: 'F j, Y',
		datetime: 'F j, Y g: i a',
		datetimeAbbreviated: 'M j, Y g: i a',
	},

Note how there's a space after the colon and before the minutes: g: i (reference PHP's datetime format).

I'm a bit confused about why this is setup the way it is. I can't think of a reason why the minutes would have a space before the hour. The only plausible explanation is that this was just a dormant bug because nobody actually used these formats in the years since? I've fixed it at 4c730f6

[github-actions]

Flaky tests detected in df5fedc.
Some tests passed with failed attempts. The failures may not be related to this commit but are still reported for visibility. See the documentation for more information.

🔍 Workflow run URL: https://github.com/WordPress/gutenberg/actions/runs/20165831866
📝 Reported issues:

• [Flaky Test] Should insert content using the global inserter #57525 in /test/e2e/specs/widgets/editing-widgets.spec.js
• [Flaky Test] should open and edit templates correctly when active_templates experiment is disabled #73743 in /test/e2e/specs/site-editor/template-id-format.spec.js

[github-actions]

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Co-authored-by: oandregal <[email protected]>
Co-authored-by: jorgefilipecosta <[email protected]>
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[oandregal]

I've rebased this PR from trunk, so it can be merged independently.

[jorgefilipecosta]

Non blocking, but should the form input bellow the calendar also follow the applied format?:

[jorgefilipecosta]

Worked well on the tests I did 👍

[oandregal]

Non blocking, but should the form input bellow the calendar also follow the applied format?:

I see how in some situations this would be handy. For example, dd/mm/yyyy vs mm/dd/yyyy. However, the date format can be anything and there's no a 1:1 match to the input field, so I'd rather leave the input field as it is.