Allow reporting errors when loading wasm modules into .NET

[cgranade]

Feature

When loading wasm modules into .NET with wasmtime, an exception is raised if a module is invalid. This exception doesn't provide any details as to what went wrong, however, making it hard to fix the module.

Implementation

The .NET implementation relies on the wasm_module_new function.
https://github.com/bytecodealliance/wasmtime/blob/121bbd36568c506a39b2dd97a95dd2b963960eb7/crates/c-api/src/lib.rs#L828

This function currently discards the error information with a match expression:

https://github.com/bytecodealliance/wasmtime/blob/121bbd36568c506a39b2dd97a95dd2b963960eb7/crates/c-api/src/lib.rs#L836

Allowing this information to be captured in a callback or in a mutable pointer to a string that could capture the Debug derive for the anyhow::Error would be helpful in diagnosing errors that occur when loading modules.

[peterhuene]

This should now be possible to fix with bytecodealliance/wasmtime#1467 merged. We can get validation errors by using the wasmtime_module_new API.

[cgranade]

Awesome, thank you for the update!