Implement crypto byte array newtypes in term of a shared type (#3684)

Introduces `CryptoBytes` type defined as:

```rust
pub struct CryptoBytes<const N: usize, Tag = ()>(pub [u8; N], PhantomData<fn() -> Tag>);
```

The type implements a bunch of methods and traits which are typically
expected from a byte array newtype
(NOTE: some of the methods and trait implementations IMO are a bit
redundant, but I decided to maintain them all to not change too much
stuff in this PR)

It also introduces two (generic) typical consumers of `CryptoBytes`:
`PublicBytes` and `SignatureBytes`.

```rust
pub struct PublicTag;
pub PublicBytes<const N: usize, CryptoTag> = CryptoBytes<N, (PublicTag, CryptoTag)>;

pub struct SignatureTag;
pub SignatureBytes<const N: usize, CryptoTag> = CryptoBytes<N, (SignatureTag, CryptoTag)>;
```

Both of them use a tag to differentiate the two types at a higher level.
Downstream specializations will further specialize using a dedicated
crypto tag. For example in ECDSA:


```rust
pub struct EcdsaTag;

pub type Public = PublicBytes<PUBLIC_KEY_SERIALIZED_SIZE, EcdsaTag>;
pub type Signature = PublicBytes<PUBLIC_KEY_SERIALIZED_SIZE, EcdsaTag>;
```

Overall we have a cleaner and most importantly **consistent** code for
all the types involved

All these details are opaque to the end user which can use `Public` and
`Signature` for the cryptos as before

substrate/frame/contracts/src/exec.rs

@@ -1466,14 +1466,14 @@ where
 
 	fn sr25519_verify(&self, signature: &[u8; 64], message: &[u8], pub_key: &[u8; 32]) -> bool {
 		sp_io::crypto::sr25519_verify(
-			&SR25519Signature(*signature),
+			&SR25519Signature::from(*signature),
 			message,
-			&SR25519Public(*pub_key),
+			&SR25519Public::from(*pub_key),
 		)
 	}
 
 	fn ecdsa_to_eth_address(&self, pk: &[u8; 33]) -> Result<[u8; 20], ()> {
-		ECDSAPublic(*pk).to_eth_address()
+		ECDSAPublic::from(*pk).to_eth_address()
 	}
 
 	#[cfg(test)]