FontSizePicker : Deprecate 36px default size

[PARTHVATALIYA]

Part of #65751

What?

Deprecate the 36px default size in FontSizePicker.

Testing Instructions

• Unit tests pass
• Storybook stories should not log console warnings
• All code snippets in documentation (JSDoc, Storybook, README) should have the __next40pxDefaultSize prop enabled

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[mirka]

Let's also add the prop to the code snippet here.

[mirka]

🚀