This commit shuffles around `*.wast`-based tests for component model
testing. All tests are now located in `tests/cli/component-model` with
subdirectories for various proposals, for example
`tests/cli/component-model-async` is now located at
`tests/cli/component-model`. Additionally async tests are disentangled
where most just require the `cm-async` feature and tests related to
`cm-async-builtins` or `cm-async-stackful` are consolidated into a
single `*.wast` test file.

The end goal is to eventually make this more amenable to upstreaming
inside of the component model repo itself by in theory just sync-ing
this one folder.