Vulkan headers: restore vulkan_fuchsia_extras.h include.
Vulkan headers: restore vulkan_fuchsia_extras.h include.

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/+/37450
Tested-by: David Turner <dcb93bd72059500c1226ad16fdd58ffe25c9e0ea@google.com>
Presubmit-Ready: David Turner <dcb93bd72059500c1226ad16fdd58ffe25c9e0ea@google.com>
Reviewed-by: Alexis Hétu <1c7141772178a7e80858c3db5052b328076f08f4@google.com>
Kokoro-Presubmit: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Kokoro-Presubmit: David Turner <dcb93bd72059500c1226ad16fdd58ffe25c9e0ea@google.com>

bkaradzic/SwiftShader,google/swiftshader,bkaradzic/SwiftShader,google/swiftshader,bkaradzic/SwiftShader,google/swiftshader,bkaradzic/SwiftShader,bkaradzic/SwiftShader