Turn the `wasmtime-runtime` crate into the `wasmtime::runtime::vm` module

[fitzgen]

We want to merge them together because there is no abstraction or layering or boundary between them in practice, and our architectures and designs have, at times, been constrained by this artificial crate boundary and what is visible in which crate and this has forced us to use nasty workarounds like defining traits in wasmtime-runtime that get implemented in wasmtime and used as dynamic trait objects inside wasmtime-runtime. Merging them will allow us to remove these hacks.

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[fitzgen]

The next step after this, before actually merging the crates together, is to factor out wasmtime_runtime::{sys,mmap,mmap_vec} into its own crate, since this functionality is used directly by the CLI in one place, and I don't want to add that stuff to the wasmtime crate's public API.

This is proving to be a bit hairier than anticipated; investigating alternatives. Shouldn't affect this PR.

[kaimast]

How do I call wasmtime_runtime::raise_user_trap after this change?

[alexcrichton]

Ah it's no longer possible to call the function after this change as it's private to the wasmtime crate. Could you detail what you were doing with the function? We can try to help out to find a workaround perhaps

[fitzgen]

Adding to what Alex said: that function was never intended to be exposed to or used by Wasmtime embedders. The wasmtime-runtime crate was an implementation detail of Wasmtime itself. Generally, to raise a trap in Wasm from a host API, you want to return an Err(..) from the host call.

[kaimast]

Generally, to raise a trap in Wasm from a host API, you want to return an Err(..) from the host call.

Oh, I did not realize that is possible. I fairly recently ported my code over from Wasmer, so I am not super familiar with API yet. That is indeed a nicer way of doing it...

Thanks for the quick responses!

[fitzgen]

@kaimast no problem! Feel free to pop into our Zulip or file an issue if you have any more questions.