[eslint-plugin] Allow defineMarker in enforce-extension

[j-malt]

What changed / motivation ?

stylex.defineMarker() will not work if not imported from a *.stylex.(ts|js) file, but if a defineMarker is exported from a StyleX file the ESLint enforce-extension rule will error with:

Only variables from stylex.defineVars() or stylex.defineConsts() can be exported from a file with a .stylex.ts extension

You can see an example of the sort of usage that would fail in the docs.

This PR extends the rule to require these functions only be exported from StyleX files.

Pre-flight checklist

• I have read the contributing guidelines
  Contribution Guidelines
• Performed a self-review of my code

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