DimensionControl: Add __next40pxDefaultSize prop

[brookewp]

Part of #46741

What?

Add a new opt-in prop __next40pxDefaultSize to DimensionControl, following the plan outlined in above mentioned PR.

Why?

For more consistency in styling.

How?

A new, temporary __next40pxDefaultSize prop. When the prop is set to true, the inputs will have a height of 40px.

Testing Instructions

In Storybook:

1. npm run storybook:dev
2. Set __next40pxDefaultSize to true for DimensionControl
3. The input height of the component should now be 40px

In the editor

Smoke test the component in the editor; DimensionControl shouldn't have any visible changes for now.

[github-actions]

Flaky tests detected in 33de2a9.
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/7122906844
📝 Reported issues:

• [Flaky Test] User Mention: should insert two subsequent mentions #48569 in /test/e2e/specs/editor/various/autocomplete-and-mentions.spec.js
• [Flaky Test] should display the "Manage Fonts" icon #56776 in /test/e2e/specs/site-editor/font-library.spec.js

[chad1008]

LGTM 🚀 🚢