ed25519_verify: Support using dalek for historical blocks (#12661)

* ed25519_verify: Support using dalek for historical blocks

The switch from `ed25519-dalek` to `ed25519-zebra` was actually a breaking change. `ed25519-zebra`
is more permissive. To support historical blocks when syncing a chain this pull request introduces
an externalities extension `UseDalekExt`. This extension is just used as a signaling mechanism to
`ed25519_verify` to use `ed25519-dalek` when it is present. Together with `ExtensionBeforeBlock` it
can be used to setup a node in way to sync historical blocks that require `ed25519-dalek`, because
they included a transaction that verified differently as when using `ed25519-zebra`.

This feature can be enabled in the following way. In the chain service file, directly after the
client is created, the following code should be added:

```
use sc_client_api::ExecutorProvider;
client.execution_extensions().set_extensions_factory(
	sc_client_api::execution_extensions::ExtensionBeforeBlock::<Block, sp_io::UseDalekExt>::new(BLOCK_NUMBER_UNTIL_DALEK_SHOULD_BE_USED)
);
```

* Fix doc

* More fixes

* Update client/api/src/execution_extensions.rs

Co-authored-by: André Silva <123550+andresilva@users.noreply.github.com>

* Fix merge and warning

* Fix docs

Co-authored-by: André Silva <123550+andresilva@users.noreply.github.com>

substrate/primitives/externalities/src/extensions.rs

@@ -89,6 +89,19 @@ macro_rules! decl_extension {
 				Self(inner)
 			}
  		}
+	};
+	(
+		$( #[ $attr:meta ] )*
+		$vis:vis struct $ext_name:ident;
+	) => {
+		$( #[ $attr ] )*
+		$vis struct $ext_name;
+
+		impl $crate::Extension for $ext_name {
+			fn as_mut_any(&mut self) -> &mut dyn std::any::Any {
+				self
+			}
+		}
 	}
 }
 
@@ -112,7 +125,7 @@ pub trait ExtensionStore {
 		extension: Box<dyn Extension>,
 	) -> Result<(), Error>;
 
-	/// Deregister extension with speicifed 'type_id' and drop it.
+	/// Deregister extension with specified 'type_id' and drop it.
 	///
 	/// It should return error if extension is not registered.
 	fn deregister_extension_by_type_id(&mut self, type_id: TypeId) -> Result<(), Error>;
@@ -179,6 +192,13 @@ impl Extensions {
 	}
 }
 
+impl Extend<Extensions> for Extensions {
+	fn extend<T: IntoIterator<Item = Extensions>>(&mut self, iter: T) {
+		iter.into_iter()
+			.for_each(|ext| self.extensions.extend(ext.extensions.into_iter()));
+	}
+}
+
 #[cfg(test)]
 mod tests {
 	use super::*;