[TS] Pack rest parameters into an array #373

Problem

The frontend records isRest, but the emitted prologue reads one parameter reference without collecting remaining arguments.

Minimal TypeScript example

export function count(...values: number[]): number {
  return values.length;
}

Expected behavior

count() returns 0 and count(1, 2) returns 2. EtsIR must represent the packed array and preserve element order.

Current source evidence

Parameter metadata; prologue.

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

Acceptance criteria

• The native TypeScript frontend emits EtsIR preserving the behavior above, including a JSON round trip.
• A focused regression checks the observable result against TypeScript/Node.js.
• Until implemented, the construct remains an explicit unsupported outcome; it is not silently represented as ordinary supported behavior.