Merge changes Idf479bed,Iee7d56c1,I23d7945e,Ibd6fa875,I52f7afb4, ...

* changes:
  vulkan: Add apk_library_dir virtual branch
  Add support for loading layers from the apk.
  Add default callbacks in the loader.
  Add support for arbitrary number of layers
  Add support for autoloading callback extension.
  Add support for multiple layers in the same so
  Add layer loading to android vulkan loader.
  Fix GetSpecific*ProcAddr.
  vulkan: Implement vk_ext_khr_*swapchain extensions
  vulkan: Add skeleton swapchain support
  vulkan: add copyright notices
  vknulldrv: Implement VkImage
  vulkan: warn on bogus CreateBuffer args