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.
