feat(theming): adds shadow variables to theme + updates styled components

[geotrev]

Description

Provides a light/dark variable set for shadow sizes small, medium, and large. Updates relevant components that currently define custom neutralHue colors with dark/light transparency overrides in v9 styles:

• Chrome – SkipNav and Header
• Draggable
• RangeInput
• PaneSplitterButton (container)
• Modals – Modal and Drawer
• Notification
• Theming – menuStyles
• Tooltip (including when isLight is given)

Checklist

• 👌 design updates will be Garden Designer approved (add the designer as a reviewer)
• 🌐 demo is up-to-date (npm start)
• ⬅️ renders as expected with reversed (RTL) direction
• 🤘 renders as expected with Bedrock CSS (?bedrock)
• 💂‍♂️ includes new unit tests. Maintain existing coverage (always >= 96%)
• ♿ tested for WCAG 2.1 AA accessibility compliance
• 📝 tested in Chrome, Firefox, Safari, and Edge

[ze-flo]

Nice clean up! 💯

[steue]

LGTM!