fix(react): drop JSX namespace import from public type declarations (#4645)

* Fix #4637: Declare React peer dependencies for posthog-js/react

* fix: declare @types/react peer, regenerate lockfile, add changeset

Unblocks CI (ERR_PNPM_OUTDATED_LOCKFILE) and closes the TypeScript half of
the same resolution gap; test no longer pins the exact version range.

* Repair PR #4638: fix: Declare React peer dependencies for posthog-js/react

* Repair PR #4638: fix: Declare React peer dependencies for posthog-js/react

* fix(react): drop JSX namespace import from public type declarations

Return ReactElement instead of JSX.Element so the emitted .d.ts typechecks
against @types/react back to 16.9.0, and correct the peer range to match.

* test: assert the @types/react floor separately from the React floor

The two peers have different minimums: hooks (16.8.0) for react, and
ReactElement's props default (16.9.0) for @types/react.

* test: decouple the @types/react floor from the React floor

The two peers share a value today but encode different constraints; record
why the types range is deliberately below what the declarations require.

* fix(react): spell return types as ReactElement<any, any>

Exactly the definition of JSX.Element, so the public types are unchanged and
@types/react stays at the 16.8.0 floor with no react/@types desync.

---------

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>