ToggleGroupControl: Add opt-in prop for 40px default size

[brookewp]

Part of #46741

What?

Add a new opt-in prop __next40pxDefaultSize to ToggleGroupControl, 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 height will be 40px instead of 36px.

Testing Instructions

In Storybook:

1. npm run storybook:dev
2. Set __next40pxDefaultSize to true
3. The height of the component should now be 40px instead of the default 36px

In the editor

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

[brookewp]

End-to-End Tests / Puppeteer - 3 (pull_request) is failing but I see it's failing when running locally against trunk.

[ciampo]

LGTM 🚀

[ciampo]

End-to-End Tests / Puppeteer - 3 (pull_request) is failing but I see it's failing when running locally against trunk.

Sounds good. We can merge this PR once the tests are passing again on trunk.

[github-actions]

Flaky tests detected in 845bdc3.
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/6776166039
📝 Reported issues:

• [Flaky Test] Overlay menu interactions in Safari (@webkit) #55816 in /test/e2e/specs/editor/blocks/navigation-frontend-interactivity.spec.js