Return an std::string_view when possible for vk::to_string functions.

[Wunkolo]

Functions that return the name of plain enums(not bit-flag enums and such that require building a new string of active bits) are just returning pointers to plaintext strings residing in .rdata, but they currently requiring allocation of a new std::string in all cases:

Vulkan-Hpp/vulkan/vulkan_to_string.hpp

Lines 3888 to 3903 in 8f9db1b

	VULKAN_HPP_INLINE std::string to_string( StructureType value )
	{
	switch ( value )
	{
	case StructureType::eApplicationInfo : return "ApplicationInfo";
	case StructureType::eInstanceCreateInfo : return "InstanceCreateInfo";
	case StructureType::eDeviceQueueCreateInfo : return "DeviceQueueCreateInfo";
	case StructureType::eDeviceCreateInfo : return "DeviceCreateInfo";
	case StructureType::eSubmitInfo : return "SubmitInfo";
	case StructureType::eMemoryAllocateInfo : return "MemoryAllocateInfo";
	case StructureType::eMappedMemoryRange : return "MappedMemoryRange";
	case StructureType::eBindSparseInfo : return "BindSparseInfo";
	case StructureType::eFenceCreateInfo : return "FenceCreateInfo";
	case StructureType::eSemaphoreCreateInfo : return "SemaphoreCreateInfo";
	case StructureType::eEventCreateInfo : return "EventCreateInfo";
	case StructureType::eQueryPoolCreateInfo : return "QueryPoolCreateInfo";

These enums in particular could be returning a std::string_view(since C++17) utilizing string-view literals so that the length of the string is known at compile-time rather than costing an additional strlen and avoids an additional string-allocation at run-time like so:

 VULKAN_HPP_INLINE std::string_view to_string( StructureType value ) 
 { 
   using namespace std::string_view_literals
   switch ( value ) 
   { 
     case StructureType::eApplicationInfo                                     : return "ApplicationInfo"sv; 
     case StructureType::eInstanceCreateInfo                                  : return "InstanceCreateInfo"sv; 
     case StructureType::eDeviceQueueCreateInfo                               : return "DeviceQueueCreateInfo"sv; 
     case StructureType::eDeviceCreateInfo                                    : return "DeviceCreateInfo"sv; 
...

With this pattern, no additional memory has to be allocated unless the user chooses to cast it to an std::string later.

[asuessenbach]

Thanks for this suggestion.
Will address it soon.

[asuessenbach]

@Wunkolo Unfortunately, all those vk::to_string functions do not only return a constant string, but have some default path returning hex-formatted value. Therefore, they can't return a std::string_view.
I realized, though, that those functions could be marked with VULKAN_HPP_CONSTEXPR_20. That is, with C++20 and above, they are constexpr, which is at least a bit.

-> #2101.