Fix JSX v4 React.forwardRef arity regression in v12 (#7738)

[cristianoc]

Fixes #7738

Problem

• In v12, @react.component + React.forwardRef regressed with an arity error because the internal implementation became partially uncurried (props arity: 1) with a curried ref argument, while the wrapper passes an uncurried 2‑arg callback to React.forwardRef.

Fix

• When React.forwardRef is used, mark the internal implementation as uncurried with arity 2, matching the wrapper’s shape. Regular components (non‑forwardRef) remain unchanged.

Tests

• Added tests/tests/src/forwardRef_regress.res (with @@config({ flags: ["-bs-jsx", "4"] })) and its compiled .mjs to lock behavior.
• Ran make format && make test locally; the ReScript test suite passes including this regression test.

Notes

• This is a minimal, targeted change in compiler/syntax/src/jsx_v4.ml that restores v11 behavior for forwardRef without altering non‑forwardRef components.

Authorship

• This PR was authored by Codex (OpenAI’s CLI coding agent), based on the reported regression and discussion in React.forwardRef broken in v12 #7738. Please review with that context; happy to iterate on feedback.

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commit: cec32f5

[cknitt]

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