Standup Skeleton Code for Cardboard Runtime

Creates features and infrastructure and initial include to begin
building the Cardboard runtime for WebXR. Currently the runtime will
simply reject all session requests, but it links in and initializes the
sdk as a proof of concept that all build files should be mostly
structured right. Stands up the following skeletons/infrastructure:
* Feature Flag and About Flags entry
* Creates CardboardDevice/Provider and adds it (and does not add the
GVR Device) based on the Cardboard Feature Flag
* Adds build files for //third_party/cardboard
* Adds VR Buildflag for Cardboard
* Creates basic directory and build file structure for cardboard
* Incorporates cardboard build into Chrome build.

Bug: 989117
Change-Id: I3e0e4349cb1a031404c38b0a6175681575c23e4b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4160186
Commit-Queue: Alexander Cooper <alcooper@chromium.org>
Reviewed-by: Alex Gough <ajgo@chromium.org>
Reviewed-by: Piotr Bialecki <bialpio@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1096488}