Summary

Implement fd_allocate for the native and web Preview1 backends.

Parent tracking issue: #15
Suggested implementation order: 15 / 39

Suggested dependencies

• Support writable virtual files and non-stdio fd_write in WASI Preview1 #21 Support writable virtual files and non-stdio fd_write in WASI Preview1

References

• https://github.com/WebAssembly/WASI/blob/wasi-0.1/preview1/docs.md#L1483

Acceptance criteria

• fd_allocate no longer returns ENOSYS on native and web.
• Tests cover allocation growth and invalid descriptor cases.