move _facetAddress to _DiamondProxy and reference in _getImplementation

Author: ItsNickBarry

contracts/proxy/diamond/_DiamondProxy.sol

@@ -25,11 +25,22 @@ abstract contract _DiamondProxy is _IDiamondProxy, _Proxy {
         override
         returns (address implementation)
     {
-        implementation = address(
+        implementation = _facetAddress(msg.sig);
+    }
+
+    /**
+     * @notice get the address of the facet associated with given selector
+     * @param selector function selector to query
+     * @return facet facet address (zero address if not found)
+     */
+    function _facetAddress(
+        bytes4 selector
+    ) internal view returns (address facet) {
+        facet = address(
             bytes20(
                 ERC2535Storage
                     .layout(ERC2535Storage.DEFAULT_STORAGE_SLOT)
-                    .selectorInfo[msg.sig]
+                    .selectorInfo[selector]
             )
         );
     }

contracts/proxy/diamond/readable/_DiamondProxyReadable.sol

@@ -200,21 +200,4 @@ abstract contract _DiamondProxyReadable is
             mstore(addresses, numFacets)
         }
     }
-
-    /**
-     * @notice get the address of the facet associated with given selector
-     * @param selector function selector to query
-     * @return facet facet address (zero address if not found)
-     */
-    function _facetAddress(
-        bytes4 selector
-    ) internal view returns (address facet) {
-        facet = address(
-            bytes20(
-                ERC2535Storage
-                    .layout(ERC2535Storage.DEFAULT_STORAGE_SLOT)
-                    .selectorInfo[selector]
-            )
-        );
-    }
 }