A previous CL updated the Vulkan headers, and removed our
include for vulkan_fuchsia_extras.h, which contains
Fuchsia-specific declarations that are used by the platform
but not upstreamed yet to Khronos.

This CL simply restores the include.

Bug: 143197472
Change-Id: I934f185c76f54e08ff52a202198cb951ad4b6644
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/37450Tested-by: David Turner <digit@google.com>
Presubmit-Ready: David Turner <digit@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Kokoro-Presubmit: David Turner <digit@google.com>