add Available since 4.1 comments

(cherry picked from commit 9a698e6b7b)

contracts/utils/Multicall.sol

@@ -6,6 +6,8 @@ import "./Address.sol";
 
 /**
  * @dev Provides a function to batch together multiple calls in a single external call.
+ *
+ * _Available since v4.1._
  */
 abstract contract Multicall {
     /**

contracts/utils/StorageSlot.sol

@@ -26,7 +26,7 @@ pragma solidity ^0.8.0;
  * }
  * ```
  *
- * Available since v4.1.0 for `address`, `bool`, `bytes32`, and `uint256`.
+ * _Available since v4.1 for `address`, `bool`, `bytes32`, and `uint256`._
  */
 library StorageSlot {
     struct AddressSlot {

contracts/utils/cryptography/ECDSA.sol

@@ -31,7 +31,7 @@ library ECDSA {
 
         // Check the signature length
         // - case 65: r,s,v signature (standard)
-        // - case 64: r,vs signature (cf https://eips.ethereum.org/EIPS/eip-2098)
+        // - case 64: r,vs signature (cf https://eips.ethereum.org/EIPS/eip-2098) _Available since v4.1._
         if (signature.length == 65) {
             // ecrecover takes the signature parameters, and the only way to get them
             // currently is to use assembly.

contracts/utils/cryptography/SignatureChecker.sol

@@ -13,6 +13,8 @@ import "../../interfaces/IERC1271.sol";
  *
  * Note: unlike ECDSA signatures, contract signature's are revocable, and the outcome of this function can thus change
  * through time. It could return true at block N and false at block N+1 (or the opposite).
+ *
+ * _Available since v4.1._
  */
 library SignatureChecker {
     function isValidSignatureNow(address signer, bytes32 hash, bytes memory signature) internal view returns (bool) {