Move outputContext from XRSession to XRRenderState

This requires all sessions that were previously setting an
outputContext in the requestSession call to move that assignment to an
updateRenderState call post-session-creation instead. Additionally,
"inline" sessions can now be created without an outputContext but must
still have one assigned to them before any requestAnimationFrame
callbacks will be processed.

Bug: 928417
Change-Id: I469fab8c3f641870387f2f92aee52182016efe37
Reviewed-on: https://chromium-review.googlesource.com/c/1476097
Commit-Queue: Brandon Jones <bajones@chromium.org>
Reviewed-by: Brian Sheedy <bsheedy@chromium.org>
Reviewed-by: Klaus Weidner <klausw@chromium.org>
Cr-Commit-Position: refs/heads/master@{#636557}
54 files changed