Initial sources for the vulkan-wsi-layer project

Initial sources for the vulkan-wsi-layer project

This commit adds the initial sources for the vulkan-wsi-layer project:
a Vulkan layer which implements some of the Vulkan window system
integration extensions such as VK_KHR_swapchain.
The layer is designed to be GPU vendor agnostic when used as part of the
Vulkan ICD/loader architecture.

The project currently implements support for VK_EXT_headless_surface and
its dependencies. We hope to extend support for further platforms such
as Wayland and direct-to-display rendering in the future.

This initial commit collects contributions from different individuals
employed by Arm.

More information on the project (building instructions, how to
contribute, etc.) can be found on the README.md file at the top of the
project tree.

Signed-off-by: Matteo Franchin <matteo.franchin@arm.com>