Check requested reference space against enabled XR session features

Currently we only check if the requested reference space is supported
by the device before resolving the request. With more detailed consent
this is no longer sufficient, we need to also check the underlying
feature of the reference space against which features have been enabled.

This CL also does some minor refactoring of code related to
XRSessionFeature.

Bug: 985095
Change-Id: Ibe6ecadbc6ce25c523eb4ee9d8a73560d8580df5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1754275
Reviewed-by: Alexander Cooper <alcooper@chromium.org>
Reviewed-by: Brandon Jones <bajones@chromium.org>
Commit-Queue: Will Cassella <cassew@google.com>
Cr-Commit-Position: refs/heads/master@{#687912}
31 files changed