Generate VulkanHeadersConfig.cmake and version file and install them.
To get the version information the header file vulkan_core.h is parsed.
In client code one can use `find_package(VulkanHeaders)` and get the
targets `Vulkan::Headers` and `Vulkan::Registry`.
The following additional files are generated and installed by CMake:
- VulkanHeadersConfig.cmake: searched for by find_package(VulkanHeaders)
- VulkanHeadersConfigVersion.cmake: provides version numbers
- VulkanHeadersTargets.cmake: CMake target definitions used by config file
