add string utils

lib/core/utils/string_utils.dart

@@ -0,0 +1,16 @@
+class StringUtils {
+  static bool emailValidation(String email) {
+    return RegExp(
+            r'^(([^<>()[\]\\.,;:\s@\"]+(\.[^<>()[\]\\.,;:\s@\"]+)*)|(\".+\"))@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\])|(([a-zA-Z\-0-9]+\.)+[a-zA-Z]{2,}))$')
+        .hasMatch(email);
+  }
+
+  static bool phoneValidation(String phone) {
+    return RegExp(r'^(\+62|62|0)8[1-9][0-9]{6,10}$').hasMatch(phone);
+  }
+
+  static bool passwordValidation(String password) {
+    return RegExp(r'^(?=.*[a-z])(?=.*[A-Z])(?=.*[0-9])(?=.*?[\W_])(?=.{8,})')
+        .hasMatch(password);
+  }
+}