[types] cursor should accept arbitrary string

[henryqdineen]

What changed / motivation ?

This updates the CSSCursor type to accept arbitrary strings to address a recent bug report. The fix in this PR is to simply add string to the union type.

I personally would prefer the TypeScript union to include | (string & {}) for the improved autocomplete but right now we are generating types from Flow. This article explains the TypeScript trick in more detail. Any objections to maintaining a separate type definitions of the CSS Types so we could use that trick? Have you considered directly using csstype?

Linked PR/Issues

Fixes #1463

Screenshots, Tests, Anything Else

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  Contribution Guidelines
• Performed a self-review of my code

[vercel]

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