`<[T, $n]>::decode` implementation can make use of TypeInfo

[gui1117]

for now it decode using an ArrayVec but this can be optimised for type with TypeInfo

parity-scale-codec/src/codec.rs

Lines 705 to 716 in 1beac25

	fn decode<I: Input>(input: &mut I) -> Result<Self, Error> {
	let mut r = ArrayVec::new();
	for _ in 0..$n {
	r.push(T::decode(input)?);
	}
	let i = r.into_inner();
	match i {
	Ok(a) => Ok(a),
	Err(_) => Err("failed to get inner array from ArrayVec".into()),
	}
	}