Implemented the "empty" constant and the "isNotEmpty()" function in the String+Empty extension.

Sources/Core/Extensions/String+Empty.swift

@@ -0,0 +1,24 @@
+//
+//  String+Empty.swift
+//  Core
+//
+//  Created by Javier Cicchelli on 15/04/2023.
+//  Copyright © 2023 Röck+Cöde. All rights reserved.
+//
+
+public extension String {
+    
+    // MARK: Properties
+    
+    /// Represents an empty string.
+    static let empty = ""
+    
+    // MARK: Functions
+    
+    /// Checks whether a string is not empty.
+    /// - Returns: A boolean value that represents whether the string is not empty.
+    func isNotEmpty() -> Bool {
+        isEmpty == false
+    }
+    
+}