chore: update to latest wasmtime release (0.38.0)

[dicej]

This updates to wasmtime v0.38.0. Because module linking support has been
removed from wasmtime as of v0.36.0, and the component model implementation is
not yet mature enough to use as a replacement (see
bytecodealliance/wasmtime#4303 for details), it is
necessary to temporarily disable the Spidermonkey tests. I've done this by
commenting-out the broken code in instantiate_smw, prefixed its name with and
underscore, and renamed the relevant host.rs files to ignore_host.rs to hide
them from the test infrastructure.

Once the component model implementation is mature enough and the broader
ecosystem has been updated to use it, we can update and restore the Spidermonkey
tests.

fixes #259

Signed-off-by: Joel Dice [email protected]

[dicej]

My original intention for #259 was to update the Spidermonkey tests to use the component model, which would hopefully serve as an example for other projects of how to migrate their code from module linking to the component model. However, Nick and Alex explained why that's not worth the effort given the current state of the ecosystem.

So this PR won't have much value for projects which use both wit-bindgen and wasmtime's old module linking support. On the contrary, it's more likely to cause pain because now such projects will be unable to upgrade wasmtime or wit-bindgen to the latest respective versions. So I hesitated to even open the PR.

Before we merge this, I'd like to know: will this be helpful to anyone, or will it just cause pain? If the latter, I'll happily close it.

[alexcrichton]

I'm gonna go ahead and merge this and it's small enough we can back out if necessary in the near future. Thanks for the PR though @dicej!