feat(dropdowns.legacy): new light/dark mode colors

[jzempel]

Description

IMPORTANT REVIEWER NOTE: due to the fact that this is a deprecated package, I took a path of minimal code disruption. Meaning 1:1 getColorV8 -> getColor replacements and:

• no $prop updates (we can decide if this needs to happen after v9 releases)
• no colorStyles & sizeStyles consolidation
• no style enhancements (such as the primary blue border for active options / focused items) to emphasize the importance of a a11y upgrade to Garden's new Combobox & Menu

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

[geotrev]

Minimal conversion feels right. Same for a risk assessment for transient props after v9 launches.

[ze-flo]

L👀KING GOOD! 💯

[steue]

LGTM!