comp: Don't initialize unused Vulkan fields with NULL
This patch set removes ~200 of redundant Vulkan struct initialization code, which results in better readability and maintainability.
The first part is to port reverting 1eae4521 to the current code base.
After this patch no compiler warnings and Vulkan validation issues are produced. This style of usage of the Vulkan API is also implemented and tested in xrdesktop.
The patch set was tested with the XCB and XCB direct mode back ends without issues.