Global Styles: Expose Labels under Form controls

[amitraj2203]

What?

Adds the label element to the Form controls screen in Global Styles.

Part of #34198. Fixes #81650.

Stacked on #81645 — this PR targets that branch and should merge after it.

Why?

Labels can be styled in theme.json since #81160, but there was no UI for it. This exposes them alongside Inputs and Selects.

How?

Adds Labels to the typography and color element lists on the Form controls screen, a description entry, and the /elements/form-controls/typography/label route.

Testing Instructions

Note: #81645's base predates #81160, so on this branch as-is the control renders but does not apply. To test, merge trunk in first — that is the state verified below, and the state that will exist once #81645 is rebased.

1. Activate a block theme and open Appearance > Editor > Styles.
2. Open Elements > Form controls.
3. Confirm Typography and Colors both list Labels, Inputs, Selects.
4. Open Labels under Typography and change the font.
5. Under Colors, set a Labels text colour, save, and confirm it applies to a <label> on the front end.

Verified locally: selecting a colour writes styles.elements.label.color.text and emits label { color: var(--wp--preset--color--accent-1); }.

Use of AI Tools

An AI coding assistant was used.

[github-actions]

Size Change: +88 B (0%)

Total Size: 7.73 MB

📦 View Changed

Filename	Size	Change
build/scripts/edit-site/index.min.js	336 kB	+17 B (+0.01%)
build/scripts/editor/index.min.js	532 kB	+71 B (+0.01%)

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