[compiler] Fix gating export misplaced on _unoptimized variant with TypeScript overload signatures

[sleitor]

Summary

When a function has TypeScript overload signatures (TSDeclareFunction nodes), the overload identifier names were treated as runtime references by Babel's isReferencedIdentifier(). This caused getFunctionReferencedBeforeDeclarationAtTopLevel to incorrectly mark the implementation as referenced before declaration, triggering the insertAdditionalFunctionDeclaration path in insertGatedFunctionDeclaration.

In that path, the original function is renamed to <fn>_unoptimized in-place, keeping any parent ExportNamedDeclaration wrapper — so the export ended up on the wrong (unoptimized) function. The new dispatcher function was inserted without export, breaking the exported binding at runtime.

Before:

// Wrong: export lands on unoptimized variant
export function useSession_unoptimized<T>(...) { ... }
// Wrong: dispatcher has no export
function useSession(arg0) { if (gate()) ... }

After:

// Correct: export is on the dispatcher
export const useSession = isForgetEnabled_Fixtures()
  ? function useSession(selector) { /* optimized */ }
  : function useSession(selector) { /* original */ };

Fix

Skip TSDeclareFunction nodes in the top-level reference traversal (the same way TSTypeAliasDeclaration is already skipped). Overload signatures are not runtime references and should not influence the reference-before-declaration detection.

Fixes #35991

Test Plan

Added compiler fixture gating-ts-overload-export.tsx covering the exported function with TypeScript overload signatures + gating + annotation mode.