Use the dev container for the WASI CI build

[brettcannon]

Keeps all WASI-related details in a single place and also helps test the container itself.

[brettcannon]

This might be annoying/tricky because https://docs.github.com/en/actions/writing-workflows/workflow-syntax-for-github-actions#jobsjob_idcontainer says we have to build on top of the GitHub action container for this to work. Otherwise we would need to run the command inside the container and then extract out the information.