Adds extensive integration tests that exercise the various ways of finding
the Vulkan-Headers.
vk-bootstrap should now use the Vulkan-Headers or Vulkan::Headers targets if
they were already defined (such as is the case of FetchContent), and will
look for the VulkanHeaders package and Vulkan package as a fallback, and will
FetchContent Vulkan-Headers directly if that fails.
This should make integration seamless with the various ways vulkan-headers
is acquired.
The vk-bootstrap-vulkan-headers target was dropped in favor of directly
linking to Vulkan-Headers (creating a target by that name if none exists).
The example triangle now will have a absolute filepath to the shaders.
This allows running the exe from directories other than the location of the shaders in the filesystem.
Alternative solutions would be to copy/paste the shader binary into the source code.
find_package is used to try to find the Vulkan-Headers, and if they aren't
present, it downloads them with fetch content. This way users don't need
vulkan 'installed' on their system, specifically for windows users.
It also changes the tests to load all the necessary function pointers, that
way we don't need to find the vulkan loader to build the tests.
Make vk-bootstrap capable of loading the vulkan runtime and not need to
link against the library. This improves the usability of vk-bootstrap since
now you don't need the vulkan library on your system to build.
This commit also changes how SystemInfo works so as to allow the dynamic
vulkan loading.
