Support u128/i128 in runtime interface (#4703)

* Support `u128`/`i128` in runtime interface

This implements support for `u128`/`i128` as parameters/return value in
runtime interfaces. As we can not pass them as identity, as for the
other primitives types, we pass them as an pointer to an `[u8; 16]` array.

* Remove some unsafe code usage

substrate/primitives/runtime-interface/test-wasm/src/lib.rs

@@ -82,6 +82,16 @@ pub trait TestApi {
 	fn overwrite_native_function_implementation() -> bool {
 		false
 	}
+
+	/// Gets an `u128` and returns this value
+	fn get_and_return_u128(val: u128) -> u128 {
+		val
+	}
+
+	/// Gets an `i128` and returns this value
+	fn get_and_return_i128(val: i128) -> i128 {
+		val
+	}
 }
 
 /// Two random external functions from the old runtime interface.
@@ -191,4 +201,14 @@ wasm_export_functions! {
 
 		assert!(test_api::overwrite_native_function_implementation());
 	}
+
+	fn test_u128_i128_as_parameter_and_return_value() {
+		for val in &[u128::max_value(), 1u128, 5000u128, u64::max_value() as u128] {
+			assert_eq!(*val, test_api::get_and_return_u128(*val));
+		}
+
+		for val in &[i128::max_value(), i128::min_value(), 1i128, 5000i128, u64::max_value() as i128] {
+			assert_eq!(*val, test_api::get_and_return_i128(*val));
+		}
+	}
 }