[iOS][Lens Overlay] Create core classes for Lens Overlay.

Creates ~empty classes that will be the core of the Lens Overlay.
There is currently no way to show or close the lens overlay. This will
be added in a follow-up CL.

Bug: 347228722
Low-Coverage-Reason: TRIVIAL_CHANGE this change doesn't contain any final logic for this feature, and just creates necessary classes
Change-Id: I383e10031a4ba719a5742db73ec2b42d05c1a6bb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5630666
Auto-Submit: Stepan Khapugin <stkhapugin@chromium.org>
Reviewed-by: Gauthier Ambard <gambard@chromium.org>
Commit-Queue: Gauthier Ambard <gambard@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1315757}