Add ERC*Pausable warning for public pausing mechanism (#4007)

Co-authored-by: Francisco <fg@frang.io>
(cherry picked from commit 1684c57)

.changeset/new-ways-own.md

@@ -0,0 +1,5 @@
+---
+'openzeppelin-solidity': patch
+---
+
+`ERC20Pausable`, `ERC721Pausable`, `ERC1155Pausable`: Add note regarding missing public pausing functionality

contracts/token/ERC1155/extensions/ERC1155Pausable.sol

@@ -13,6 +13,12 @@ import "../../../security/Pausable.sol";
  * period, or having an emergency switch for freezing all token transfers in the
  * event of a large bug.
  *
+ * IMPORTANT: This contract does not include public pause and unpause functions. In
+ * addition to inheriting this contract, you must define both functions, invoking the
+ * {Pausable-_pause} and {Pausable-_unpause} internal functions, with appropriate
+ * access control, e.g. using {AccessControl} or {Ownable}. Not doing so will
+ * make the contract unpausable.
+ *
  * _Available since v3.1._
  */
 abstract contract ERC1155Pausable is ERC1155, Pausable {

contracts/token/ERC20/extensions/ERC20Pausable.sol

@@ -12,6 +12,12 @@ import "../../../security/Pausable.sol";
  * Useful for scenarios such as preventing trades until the end of an evaluation
  * period, or having an emergency switch for freezing all token transfers in the
  * event of a large bug.
+ *
+ * IMPORTANT: This contract does not include public pause and unpause functions. In
+ * addition to inheriting this contract, you must define both functions, invoking the
+ * {Pausable-_pause} and {Pausable-_unpause} internal functions, with appropriate
+ * access control, e.g. using {AccessControl} or {Ownable}. Not doing so will
+ * make the contract unpausable.
  */
 abstract contract ERC20Pausable is ERC20, Pausable {
     /**

contracts/token/ERC721/extensions/ERC721Pausable.sol

@@ -12,6 +12,12 @@ import "../../../security/Pausable.sol";
  * Useful for scenarios such as preventing trades until the end of an evaluation
  * period, or having an emergency switch for freezing all token transfers in the
  * event of a large bug.
+ *
+ * IMPORTANT: This contract does not include public pause and unpause functions. In
+ * addition to inheriting this contract, you must define both functions, invoking the
+ * {Pausable-_pause} and {Pausable-_unpause} internal functions, with appropriate
+ * access control, e.g. using {AccessControl} or {Ownable}. Not doing so will
+ * make the contract unpausable.
  */
 abstract contract ERC721Pausable is ERC721, Pausable {
     /**