Improve Dispatch Errors

[jsdw]

Dispatch errors are a bit pants; we only decode the Module variant, and then we cloned a bunch of details out of metadata into it. This PR makes the following changes:

• Expose more dispatch error details; this is important since token errors are now separate from module errors, and are quite a likely thing people might want to react to.
• Use the DispatchError in our dry_run result too, so we get the same level of detail there (for dispatch erros at least).
• Re-work ModuleError API; don't pull/clone things from metadata; call that on-demand instead.
• Use DecodeAsType to decode DispatchErrors based on shape, so we don't have to worry about indexes changing if variants are added.
• Mark all errors #[non_exhaustive] to future proof a little against new variants being added (with DecodeAsType, this at least gives us a path to add new variants and deprecate old ones without worrying about index stuff).

[niklasad1]

I think this is better, &str implies only static &str which is not that flexible to use.

Suggested change

	impl From<&str> for Error {
	impl<T: AsRef<str>> From<T> for Error {

[jsdw]

But impl From<T> I think would conflict with all of the other From<InnerError> impls we have on Error :(

Let me double check that..

[jsdw]

Ok nar that didn't work; conflicting impls!

I also did a test and this code worked fine:

fn test() {
    let s = String::from("hello");
    let r = s.as_str();
    let _e = Error::from(r);
}

So I think the From<&str> impl does not require &'static str :)

(now I look at it I am surprised that I didn't have to provide an explicit lifetime there)

[niklasad1]

Ok, I did exactly the same for a while ago and rustc inferred it as 'static maybe just me then :)

[jsdw]

I put an explicit lifetime on this to make it clear, and because I'm surprised I didn't need one already!

[niklasad1]

👍

[lexnv]

LGTM!