layers: Add VK_EXT_external_semaphore_drm_syncobj

[mahkoh]

KhronosGroup/Vulkan-Docs#2692

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[spencer-lunarg]

@mahkoh this looks good, I know the VVL coverage was very minimal, for sake of making everyone's life easy, feel free to just leave this here, and when the extension is added, we will pull it VVL with a header update (all the generated code) and then you can just rebase this, with the new generated VUs and we should be good to go

The only thing I will ask then (not now, but before merging) is to

1. Add a test to make sure the VUs get triggered
2. Add 1 positive test using the extension correctly, this greatly reduces false positive regressions in VVL