External memory fd implementation

[SupaMaggie70Incorporated]

Connections
#7819
Builds on #7825

Description
This allows to import external memory from unix file descriptors, through the VK_KHR_external_memory_fd extension.

Current issues:

• Do we actually want to expose this kind of functionality?
• This is very similar to VK_KHR_external_memory_win32, when support for that is added more fully, how should this be affected?
• No validation
• Lots of copy pasted code rather than shared functions
• Every import call makes a vulkan instance call on the physical device, rather than caching these or making them at device creation time. I am happy to discuss my reasoning for this with anyone who asks, but as of right now it isn't clear how necessary this approach is.

Testing
Currently untested, hence the draft status.

Squash

Checklist

• Run cargo fmt.
• Run taplo format.
• Run cargo clippy --tests. If applicable, add:
  • --target wasm32-unknown-unknown
• Run cargo xtask test to run tests.
• If this contains user-facing changes, add a CHANGELOG.md entry.