Widgets: Use --wpds-cursor-control design token

[himanshupathak95]

What?

Part of #76221

Why?

Update the instance of cursor: pointer to use the --wpds-cursor-control design token so interactive control cursor behavior can be centrally configured.

How?

Replaced hardcoded cursor: pointer with cursor: var(--wpds-cursor-control) in the Legacy Widget block's editor stylesheet.

Testing Instructions

1. Open the Widgets editor and add a Legacy Widget block in the block editor.
2. Hover over the widget preview/no-preview area.
3. Inspect the element and verify cursor: var(--wpds-cursor-control) is applied.
4. Confirm cursor behavior is unchanged (still shows pointer via build-time fallback).

Screenshots or screencast

Before

After

[github-actions]

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[mirka]

Looks good 👍