Replace libsecp256k1 with secp256k1 (#10798)

* Replace libsecp256k1 with secp256k1

* Wipe ecdsa secret key from memory on drop

* Some comments for a known issue

* Safer core crypto primitives `from_slice` constructor

Previous version panics if slice lenght is not the expected one.

* Unit test fix

* Enable use of global secp256k1 context

* Better comments for ecdsa `Pair` drop

* Replace `libsecp256k1` with `seco256k1` in `beefy-mmr`

Used to convert ecdsa public key to ETH address

* Replace `libsecp256k1` with `secp256k1` in FRAME `contracts`benchmarks

* Temporary rollback of `beefy-mmr` to libsecp256k1

Check for detected build issues

* Cargo fmt

* Rollback of FRAME `contracts` benchmarks to `libsecp256k1`

* Rollback for unrelated changes

* Typo fix

* Add comments for deprecated `ecdsa_verify` and `secp256k1_ecdsa_recover`

substrate/primitives/core/src/sr25519.rs

@@ -341,10 +341,13 @@ impl Signature {
 	///
 	/// NOTE: No checking goes on to ensure this is a real signature. Only use it if
 	/// you are certain that the array actually is a signature. GIGO!
-	pub fn from_slice(data: &[u8]) -> Self {
+	pub fn from_slice(data: &[u8]) -> Option<Self> {
+		if data.len() != 64 {
+			return None
+		}
 		let mut r = [0u8; 64];
 		r.copy_from_slice(data);
-		Signature(r)
+		Some(Signature(r))
 	}
 
 	/// A new instance from an H512.