Enhance testing of nondeterministic host functionality with component composition

In https://github.com/WebAssembly/wasi-libc/pull/764 I added a test for getaddrinfo, but given the flaky nature of DNS servers the test doesn't actually assert either success or failure. With components, however, what we could do is instead build a component which provides the associated WASI interface and make that part of the test. That way we'd still test libc but we wouldn't actually test any live DNS servers.

In general this is a pretty good way to expand the scope of testing in wasi-libc. This would enable testing precise behaviors of certain APIs and certain behaviors, which might be ever-yet-more-relevant with WASIp3 and async thrown into the mix.

This is a pretty large refactoring of the test suite, however, so I'm not bundling this as part of #764, but wanted to track this nonetheless as an idea of expanding the scope of testing.

Start with the getaddrinfo test added in pull request #764 and examine how it currently avoids asserting DNS success or failure. Investigate component composition that provides the associated WASI interface, then define the test-suite refactoring needed to exercise libc without live DNS servers. Done means the approach supports precise API behavior tests without relying on nondeterministic hosts.