fix(loading): updated storybook controls, mdx, default props and tests

[sstrubberg]

Closes #12162

Updated Storybook Controls and MDX. Also went in and moved the defaultProps to default params and updated the public API snapshot for fun-sies.

Changelog

Changed

• Renamed .story -> .stories
• Removed the knobs, moved to controls
• Updated the MDX to show the goods
• In the component itself moved the defaultProps to default params
• Updated the Public API snapshot to reflect the new defaults params.

Testing / Reviewing

Hit up the Loading component in Storybook. Controls should work as expected. The docs tab should show the MDX.

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[abbeyhrt]

Looks good to me!