Support Vulkan on Linux as well as Windows.
Refactor display and surface classes into Win32 and Linux parts and
add Linux parts to gn and gyp builds.
BUG=angleproject:1668
Change-Id: I2a7d29c35f4f42fa0035bd97938d3770f3627672
Reviewed-on: https://chromium-review.googlesource.com/412426
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
