Add field names to pallet Event variants (#9993)

* convert pallet-assets events to struct types

* updated events of a couple pallets

* updated pallet event field names

* update pallet event field names

* updated events in test files

* cargo fmt

* minorfixes

* fix assertion error

* minor fix

* formatting fix

* fmt

substrate/frame/staking/src/slashing.rs

@@ -190,7 +190,7 @@ pub(crate) struct SpanRecord<Balance> {
 impl<Balance> SpanRecord<Balance> {
 	/// The value of stash balance slashed in this span.
 	#[cfg(test)]
-	pub(crate) fn amount_slashed(&self) -> &Balance {
+	pub(crate) fn amount(&self) -> &Balance {
 		&self.slashed
 	}
 }