Support for Wasm Coredump

#### Feature

When the Wasm instance traps, it's sometimes difficult to understand what happened. Post-mortem debugging using coredumps (which is extensively used in native environment) would be helpful for investigating and fixing crashes.

Wasm coredump is especially useful for serverless environment where production binaries are stripped and/or have access to limited logging.

#### Implementation

Implement Wasm coredumps as specified by https://github.com/WebAssembly/tool-conventions/blob/main/Coredump.md.
Note that the spec is early and subject to changes. Feedback very welcome!

cc @fitzgen

Start by reading the linked WebAssembly Coredump specification and its requirements for trapped Wasm instances and post-mortem debugging. Then identify the relevant Wasmtime trap and runtime paths; done means implementing the specification sufficiently to produce usable coredumps and validating the behavior against the project’s tests.

Written by the indexing model from the issue text.