[iOS] Create GLIC Promo Infra Part 2

This CL:
- Registers GLICPromoDisplayHandler in
registerStandardPromoDisplayHandlerPromos
- Implements a basic scene agent to pipe promo manager infra
- Starts scene agent behind kPageActionMenu flag in scene controller

This CL was meant to have incomplete code in order to make the CL size
smaller.

Follow up from: crrev.com/c/6505700

Fixed: 414805017
Change-Id: I82e784748f68ac632bc0b3b2a41ba6ec5faf4133
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6508351
Reviewed-by: Mark Cogan <marq@chromium.org>
Reviewed-by: Robbie Gibson <rkgibson@google.com>
Commit-Queue: Joemer Ramos <joemerramos@google.com>
Cr-Commit-Position: refs/heads/main@{#1456980}