[ChromeVox] Convert PanelNodeMenuBackground to TypeScript

AX-Relnotes: n/a.
Bug: b/267329383
Change-Id: Idb88bed07ae82f13197e2763583045f96cdd6f5f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5577947


Reviewed-by: Jacob Francis <francisjp@google.com>
Auto-Submit: Anastasia Helfinstein <anastasi@google.com>
Commit-Queue: Anastasia Helfinstein <anastasi@google.com>
Cr-Commit-Position: refs/heads/main@{#1313608}