Add external object extensions for Fuchsia to GL API Add extensions layered on top of GL_EXT_memory_object and GL_EXT_semaphore to support GL & Vulkan interoperation on Fuchsia. They are analagous to the file descriptor versions, except not quite as opaque. This is a draft; the underlying vulkan extensions have not been submitted to Khronos. Bug: angleproject:3492 Change-Id: Ic4723ded9fff752c4186eaa6a7f07d9ac51a3364 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1642332 Commit-Queue: Michael Spang <spang@chromium.org> Reviewed-by: Geoff Lang <geofflang@chromium.org>