[TS] Evaluate computed keys in destructuring bindings #384

Problem

A computed object-binding key is not lowered as an evaluated runtime property name.

Minimal TypeScript example

export function pick(input: Record<string, number>, key: string): number {
  const { [key]: value } = input;
  return value;
}

Expected behavior

pick({x:3}, "x") returns 3. Evaluate key once and bind the value of that property. Keep this separate from computed keys in object-literal construction.

Current source evidence

Binding-pattern lowering.

Checked against JacoDB neo 873f8e99faf3f1e4736935be96ce1c319985c574. This exact snippet is a proposed regression from source audit; it has not yet been run as a new end-to-end test.

Acceptance criteria

• A native-frontend regression verifies the relevant EtsIR shape and JSON round trip.
• The example's observable result/evaluation order agrees with TypeScript/Node.js when a consuming execution model is available.
• Until implemented, the frontend reports this construct as unsupported rather than silently substituting unrelated semantics.