Simplify runtime api error handling (#8114)

* Ahh

* Work work work

* Fix all the compilation errors

* Fix test

* More fixes...

substrate/client/service/test/src/client/light.rs

@@ -215,7 +215,7 @@ impl CallExecutor<Block> for DummyCallExecutor {
 			Result<NativeOrEncoded<R>, Self::Error>
 		) -> Result<NativeOrEncoded<R>, Self::Error>,
 		R: Encode + Decode + PartialEq,
-		NC: FnOnce() -> Result<R, String> + UnwindSafe,
+		NC: FnOnce() -> Result<R, sp_api::ApiError> + UnwindSafe,
 	>(
 		&self,
 		_initialize_block_fn: IB,

substrate/client/service/test/src/client/mod.rs

@@ -1327,7 +1327,9 @@ fn doesnt_import_blocks_that_revert_finality() {
 
 	let import_err = client.import(BlockOrigin::Own, b3).err().unwrap();
 	let expected_err = ConsensusError::ClientImport(
-		sp_blockchain::Error::NotInFinalizedChain.to_string()
+		sp_blockchain::Error::RuntimeApiError(
+			sp_api::ApiError::Application(Box::new(sp_blockchain::Error::NotInFinalizedChain))
+		).to_string()
 	);
 
 	assert_eq!(