Ability to create a buffer with data

[kvark]

It could be very convenient, e.g. when loading a model from GLTF, to create a buffer and provide data, without carrying around a command encoder and keeping track of temporary buffers.

Support-wise, it's already built into Metal and OpenGL. However, on Vulkan we'd need to have a mechanism for "internal submission".
The other downside is that this path will never be optimal on Vulkan: ideal scenario would have the user filling out a mapped region of data instead of providing a CPU pointer to start with.

Status: in consideration