Discussion regarding a WASI embedding API (wasi-c-api)

Moving the discussion from https://github.com/WebAssembly/wasm-c-api/issues/122 to this repo.

The Wasm C API allows embedders to embed a Wasm engine to instantiate Wasm modules, providing imports to the module.

However, the Wasm C API has no understanding of WASI's existence and that's probably for the best. As @sbc100 and @rossberg suggested, perhaps there is a need for a "WASI C API" for embedding WASI-implementing WebAssembly engines. This would allow embedders to reuse the engine's WASI implementation without having to import their own when using the Wasm C API.

This API would likely be an extension to the Wasm C API that would allow:

• The configuration of WASI (preopens, argv, environ, etc.) on a per-module basis.
• The ability to instantiate (see wasm_instance_new in the Wasm C API) a module with WASI imports (all or some supported subset).

While this doesn't pertain to WASI itself, I think this repo is the best place to kick off a discussion on this topic.

Start by reading the linked wasm-c-api issue 122 and the Wasm C API entry point wasm_instance_new. Compare the proposed per-module configuration and WASI-import instantiation requirements with the existing API discussion. Done means reaching an agreed direction for the embedding API, rather than making a defined code change.