Add a new host function for reporting fatal errors; make WASM backtraces readable when printing out errors (#10741)

* Add a new host function for reporting fatal errors

* Fix one of the wasmtime executor tests

* Have `#[runtime_interface(wasm_only)]` actually mean WASM-only, and not no_std-only

* Print out errors through `Display` instead of `Debug`

* Switch one more trait to require `Error` for its error instead of only `Debug`

* Align to review comments

substrate/primitives/consensus/common/src/lib.rs

@@ -98,7 +98,7 @@ pub trait Environment<B: BlockT> {
 		+ Unpin
 		+ 'static;
 	/// Error which can occur upon creation.
-	type Error: From<Error> + std::fmt::Debug + 'static;
+	type Error: From<Error> + std::error::Error + 'static;
 
 	/// Initialize the proposal logic on top of a specific header. Provide
 	/// the authorities at that header.
@@ -191,7 +191,7 @@ mod private {
 /// Proposers are generic over bits of "consensus data" which are engine-specific.
 pub trait Proposer<B: BlockT> {
 	/// Error type which can occur when proposing or evaluating.
-	type Error: From<Error> + std::fmt::Debug + 'static;
+	type Error: From<Error> + std::error::Error + 'static;
 	/// The transaction type used by the backend.
 	type Transaction: Default + Send + 'static;
 	/// Future that resolves to a committed proposal with an optional proof.