Change structure member sType to non-const to allow default assignment operator. Make copy constructor and copy assignment default. The latter is required for C++20 designated initializers. Delegate the constructor from C-type to the copy constructor by casting rhs accordingly. Fix warnings on gcc/clang.

tests/ArrayProxy/ArrayProxy.cpp

@@ -18,9 +18,6 @@
 #include "vulkan/vulkan.hpp"
 #include <iostream>
 
-static char const* AppName = "ArrayProxy";
-static char const* EngineName = "Vulkan.hpp";
-
 void fct(vk::ArrayProxy<int> /*ap*/)
 {}