[iOS][QD] Make BrowserCoordinator be the owner of QDCoordinator

This is a preparatory CL to https://crrev.com/c/5483451. As
QDViewController should manage its own navigation controller (see
https://crrev.com/c/5483451), we'll make the BrowserCoordinator its
owner.

Bug: 335387869
Change-Id: I60ccf98555a7a6e32798c28c1118aaee56011f59
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5490727
Reviewed-by: Gauthier Ambard <gambard@chromium.org>
Commit-Queue: Filipa Senra <fsenra@google.com>
Cr-Commit-Position: refs/heads/main@{#1296000}