Add warning about unsupported smart insert

Author: seaburg

Example/Example/Base.lproj/Main.storyboard

@@ -20,9 +20,10 @@
                         <autoresizingMask key="autoresizingMask" widthSizable="YES" heightSizable="YES"/>
                         <subviews>
                             <textField opaque="NO" clipsSubviews="YES" contentMode="scaleToFill" contentHorizontalAlignment="left" contentVerticalAlignment="center" borderStyle="roundedRect" placeholder="_ (___) ____ ____" textAlignment="natural" minimumFontSize="17" translatesAutoresizingMaskIntoConstraints="NO" id="vrS-aj-jzx" customClass="FormattedTextField" customModule="Example" customModuleProvider="target">
+                                <rect key="frame" x="16" y="40" width="343" height="30"/>
                                 <nil key="textColor"/>
                                 <fontDescription key="fontDescription" type="system" pointSize="20"/>
-                                <textInputTraits key="textInputTraits"/>
+                                <textInputTraits key="textInputTraits" smartInsertDeleteType="no"/>
                                 <userDefinedRuntimeAttributes>
                                     <userDefinedRuntimeAttribute type="string" keyPath="textMask" value="+× ××× ××× ××××××××"/>
                                 </userDefinedRuntimeAttributes>

FormattedTextField/FormattedTextField.swift

@@ -47,8 +47,13 @@ open class FormattedTextField: UITextField {
         } else if let placeholder = super.placeholder {
             placeholderLabel.text = placeholder
         }
-        // iOS 11: placeholderRect(forBounds:) returns empty rect when placeholder is empty
-        super.placeholder = " "
+        if #available(iOS 11, *) {
+            // iOS 11: placeholderRect(forBounds:) returns empty rect when placeholder is empty
+            super.placeholder = " "
+            if smartInsertDeleteType != .no {
+                print("[FormattedTextField] warning: smartInsertDeleteType unsupports");
+            }
+        }
 
         addSubview(placeholderLabel)
     }