Vulkan: Implement glImportMemoryFdEXT Allow importing opaque file descriptors into memory objects on linux. Currently this just holds onto the file descriptor rather than calling vkAllocateMemory immediately. The latter will be easier once we have support for suballocation (anglebug.com/2162). Bug: angleproject:3289 Change-Id: Ia80ce07b2a9ec95b9063feb9bfeb24ffe77fa40e Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1552028 Commit-Queue: Michael Spang <spang@chromium.org> Reviewed-by: Geoff Lang <geofflang@chromium.org>