FEMU isn't reporting zircon events correctly in
vkGetPhysicalDeviceExternalSemaphorePropertiesKHR, which causes the
tests to be skipped. There's no test that can catch this problem, so add
one.

Bug: angleproject:4625
Change-Id: I0733e84eccb630569230c360fb900a1f04bf0f9b
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2195690
Commit-Queue: Michael Spang <spang@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>