Split types out of theming-ramp into new theme types package

[JasonVMo]

Platforms Impacted

• iOS
• macOS
• win32
• windows
• android

Description of changes

This creates a new package, @fluentui-react-native/theme-types that contains all of the typing information for the theme. This has a number of benefits:

• The package is typing only, which means that it can be imported with a minimal impact on bundle size if someone only needs the types
• This also allows the opportunity to explore alternative implementations for the theming parts without messing with the core packages

Verification

This should be mechanical (I know, famous last words) so automated tests should be sufficient

Before	After
Screenshot or description before this change	Screenshot or description with this change

Pull request checklist

This PR has considered (when applicable):

• Automated Tests
• Documentation and examples
• Keyboard Accessibility
• Voiceover
• Internationalization and Right-to-left Layouts

[ghost]

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