This simplifies NextArrowFunctionInfo, allows us to Scope::Snapshot::Reparent
directly rather than moving it, and allows us to skip reparenting in the simple
parameter arrow function cases.

This CL additionally fixes arrow function name inferring.

Change-Id: Ie3e5ea778f3d7b84b2a10d4f4ff73931cfc9384a
Reviewed-on: https://chromium-review.googlesource.com/c/1386147Reviewed-by: Igor Sheludko <ishell@chromium.org>
Commit-Queue: Toon Verwaest <verwaest@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58405}