fix(styles): update notification to new token format

[joshblack]

Part of #9358

Our component token strategy currently requires teams to pass in the component tokens to the theme mixin directly in order for component tokens to work across themes. This PR updates notification so that its component tokens work in different themes and introduces a way to automatically register component tokens in the theme.

Changelog

New

• Add support for local component tokens to themes package
• Add support for getting a CSS Custom property for a component token

Changed

• Update eslint config to ignore *.stories.js files for prop type warnings
• Update storybook to use the correct background token
• Update notification story to include playground for toast
• Move all notification style tests into one test file
• Update notification to new token format, automatically register tokens

Removed

Testing / Reviewing

• Visit the notification playground story
• Turn on lowContrast in controls
• Switch between themes
• Verify that the background of the notification changes and the text remains readable

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[tay1orjones]

Awesome! The toast notification playground story looks great 🎉

[tw15egan]

Works great 🎉