API subset generation

[t-artikov]

While Vulkan (with extensions) contains a vast number of features, usually only a fraction of them are used in a particular project. I suggest adding the ability to specify the API version and a list of extensions for VulkanHppGenerator. For example:
./VulkanHppGenerator -api-version 1.1 -extensions VK_KHR_swapchain,VK_EXT_debug_utils
The resulting header files will only contain the specified functionality.

This offers the following benefits:

• Reduced compilation time.
• Improved runtime performance - no need to resolve and store unnecessary function pointers.
• Enhanced usability - less noise in IDE autocomplete hints.

[asuessenbach]

That's an interesting approach for those who regularly build their vulkan.hpp on their own, instead of just using what's provided by the Vulkan SDK.
Of course, when specifying an api-version, all versions up to that version would be generated.
And when specifying an extension, all extensions (and potentially versions) that extension depends on would be generated as well.

But I think, this would be approached with low priority:

• On reduced compilation time: this is probably a non-issue when you're using C++20-modules, which is supported by Vulkan-Hpp now.
• On improved runtime performance: I doubt that this is worth such an effort. It would reduce the number of functions to resolve and store by a few dozens. Resolving is done once or twice on start-up, and a few dozen function pointers is not that much memory to gain.
• On enhanced usability: agreed, that could be real benefit.