HDR: Add max luminance to gfx::DisplayColorSpaces

Don't populate or use this yet. Rename the SDR maximum luminance to
indicate units.

Remove HDRStaticMetadata from gfx::DisplayColorSpaces, since it's not
being used (and was missing from things like the equality operator).

Bug: 1286074
Change-Id: I9abc660e06d0daf992d66fd72c1f96644c20919a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3378533


Reviewed-by: Robert Sesek <rsesek@chromium.org>
Reviewed-by: Zhenyao Mo <zmo@chromium.org>
Commit-Queue: ccameron chromium <ccameron@chromium.org>
Cr-Commit-Position: refs/heads/main@{#958197}