chore: upgrade styled components v6 xstyled v4

[mleralec]

Upgrade guide

• Upgrade styled-components to v6
• Upgrade @xstyled/styled-components to v4
• Remove @types/styled-components (types are now included in styled-components@6.*.*)
• Use styled.whateverBox instead of styled.div with ${system} pattern (The definition of the return type of the styled function has change)

const StyledTest = styled.div`
  ${system}
`
const Test = () => <Test backgroundColor="tomato" />

This snippet will throw an error because the prop backgroundColor doesn't exit on StyledTest

To fix the error, you need to use the following pattern:

const StyledTest = styled.box``
// or
const StyledTest = styled.div<WuiProps>`
  ${system}
` 

Those two snippets are equivalent, please use the first one (more concise)

• Update the rule toHaveStyleRule on test by adding spaces on rgb/rgba keywords:

- expect(yourElement).toHaveStyleRule('color', 'rgba(0,0,0,1)')
+ expect(yourElement).toHaveStyleRule('color', 'rgba(0, 0, 0, 1)')

Other breaking changes:

• Removed deprecated stuff on @welcome-ui/system
• Some changes on theme cf 1736741

[github-actions]

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[mleralec]

cc @theo-mesnil what is the secondary-red color? 🤔

[theo-mesnil]

An invention (it's the next colors but it's not ok here :D)

[theo-mesnil]

@mleralec it's fixed here #2539