Made private methods internal to allow for overriding (#2027)

* Made private methods internal to allow for overriding

* Revert package.lock changes.

* Make _move private again

* Expose the ERC1820 registry address

* Add changelog entry

Co-authored-by: Nicolás Venturo <nicolas.venturo@gmail.com>

CHANGELOG.md

@@ -10,6 +10,7 @@
 ### Improvements
  * `ERC777`: `_burn` is now internal, providing more flexibility and making it easier to create tokens that deflate. ([#1908](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/1908))
  * `ReentrancyGuard`: greatly improved gas efficiency by using the net gas metering mechanism introduced in the Istanbul hardfork. ([#1992](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/1992), [#1996](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/1996))
+ * `ERC777`: improve extensibility by making `_send` and related functions `internal`. ([#2027](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2027))
  * `ERC721`: improved revert reason when transferring tokens to a non-recipient contract. ([#2018](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2018))
 
 ### Breaking changes

contracts/token/ERC777/ERC777.sol

@@ -28,7 +28,7 @@ contract ERC777 is Context, IERC777, IERC20 {
     using SafeMath for uint256;
     using Address for address;
 
-    IERC1820Registry constant private ERC1820_REGISTRY = IERC1820Registry(0x1820a4B7618BdE71Dce8cdc73aAB6C95905faD24);
+    IERC1820Registry constant internal ERC1820_REGISTRY = IERC1820Registry(0x1820a4B7618BdE71Dce8cdc73aAB6C95905faD24);
 
     mapping(address => uint256) private _balances;
 
@@ -350,7 +350,7 @@ contract ERC777 is Context, IERC777, IERC20 {
         bytes memory operatorData,
         bool requireReceptionAck
     )
-        private
+        internal
     {
         require(from != address(0), "ERC777: send from the zero address");
         require(to != address(0), "ERC777: send to the zero address");
@@ -408,7 +408,7 @@ contract ERC777 is Context, IERC777, IERC20 {
         emit Transfer(from, to, amount);
     }
 
-    function _approve(address holder, address spender, uint256 value) private {
+    function _approve(address holder, address spender, uint256 value) internal {
         // TODO: restore this require statement if this function becomes internal, or is called at a new callsite. It is
         // currently unnecessary.
         //require(holder != address(0), "ERC777: approve from the zero address");
@@ -435,7 +435,7 @@ contract ERC777 is Context, IERC777, IERC20 {
         bytes memory userData,
         bytes memory operatorData
     )
-        private
+        internal
     {
         address implementer = ERC1820_REGISTRY.getInterfaceImplementer(from, TOKENS_SENDER_INTERFACE_HASH);
         if (implementer != address(0)) {
@@ -463,7 +463,7 @@ contract ERC777 is Context, IERC777, IERC20 {
         bytes memory operatorData,
         bool requireReceptionAck
     )
-        private
+        internal
     {
         address implementer = ERC1820_REGISTRY.getInterfaceImplementer(to, TOKENS_RECIPIENT_INTERFACE_HASH);
         if (implementer != address(0)) {