Paragraph: Add text column support

[scruffian]

What?

Closes #27118

Enables columns support in a paragraph block

Why?

This is a useful control for the paragraph block.

How?

Add support for textColumns to the block

Testing Instructions

1. Select a paragraph block
2. Enable columns in the paragraph typography block
3. Confirm that changes to the number of columns are reflected in the frontend and editor

Screenshots or screencast

[github-actions]

Flaky tests detected in e8a817b.
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/21034285705
📝 Reported issues:

• [Flaky Test] should allow user to add and remove multiple local font files #62862 in /test/e2e/specs/admin/font-library.spec.js

[mikachan]

These changes look good to me, but it looks like the test failure is a genuine related failure, and I think we'll need a backport PR for the changes in lib/class-wp-theme-json-gutenberg.php.

[github-actions]

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[tellthemachines]

LGTM and works really well with the recently added wide/full alignment!

The theme json class changes will need a trac ticket + wp-develop PR and then adding PR link to backport changelog, which should make the CI check pass.

[t-hamano]

Thanks for the PR! Overall, it looks good to me, but I have left some feedback.

[t-hamano]

What is the reason for this change? Is this related to the type markers introduced in #73452? I guess it will work fine even if left null.

cc @ramonjd

[scruffian]

Removed, thanks

[t-hamano]

We need to keep this code as is 😅 ('textColumns' => null), otherwise the textColumns setting will be considered invalid, and the UI will not be able to disable it.

Without this code, we can't disable the UI using a theme.json like this:

{
	"version": 3,
	"settings": {
		"appearanceTools": true,
		"layout": {
			"contentSize": "840px",
			"wideSize": "1100px"
		},
		"typography": {
			"textColumns": false
		}
	}
}

[bph]

Just added the label Needs Dev Note as the theme.json updates would help theme developer to get a hang of the new feature. It could be part of a possible roundup post of theme.json updates.