Add automated tests for Wasmi's C-API

[Robbepop]

Wasmi experimentally supports the official Wasm C-API.

However, the state of Wasmi's implementation is experimental, mostly due to missing automated tests.
I am currently not sure how other runtimes, e.g. Wasmtime and Wasmer are implementing automated tests for their C-APIs but it would certainly be nice if there was a testsuite like there exists for Wasm and WASI.

For a start it could be enough to add a CI job to ensure compilation and linking of Wasmi's C-API is working as expected on all major platforms, e.g. ubuntu-latet, windows-latest and macos-latest.
So far we only have a small CI test here: https://github.com/wasmi-labs/wasmi/blob/main/.github/workflows/rust.yml#L59

Resolving this issue allows us to flag Wasmi's C-API support as stable.

cc @turbolent (#1298 (comment))