C++20 module name

[M2-TE]

The module is currently set to vulkan_hpp, which doesn't really adhere to any of the, frankly still developing, naming schemes for modules. Since it is still experimental, I would like to propose changing the module name and wanted to hear some thoughts on it.

1. vulkan.hpp: Module names are officially allowed to include dots, often eluding to paths. A module in foo/faa.cppm could be exported as export module foo.faa to prevent module name clashes and also "categorize" it. This does not really apply here, as we can cram everything into a single module, so it can instead be used to signify the kind of vulkan headers that are being imported. Namely hinting at the hpp portion.
2. vulkan: Choosing plain old vulkan might be the nicest option as C does not have any modules at all. It would be very clear intent (importing C++ headers) and also concise. Also suits the vulkan namespace that everything is in.

I personally would love to simply have import vulkan as the concise option, particularly if we may want to merge the video module into the main one as per #2310.

[sharadhr]

The initial PR (#1582) that first introduced the module called it module vulkan. This was then changed in #1651. I'm not entirely sure why and personally I also prefer module vulkan.

[asuessenbach]

Actually, I'd be fine with any of the proposed names.

I had switched to vulkan_hpp to be "closer" to the project's name, Vulkan-Hpp. But as @M2-TE said: "C does not have any modules at all", and this is the C++-binding, simply using vulkan sounds reasonable as well.

That is, because of the still somewhat experimental nature, if any of you would craft a little PR for this, I'd happy to merge that.