Add focus and blur support to InputNumber (#7615)

* Add focus support to InputNumber

* Convert string ref to private ref

* Added blur method and fixed linting

components/input-number/index.tsx

@@ -28,6 +28,8 @@ export default class InputNumber extends React.Component<InputNumberProps, any>
     step: 1,
   };
 
+  private inputNumberRef: any;
+
   render() {
     const { className, size, ...others } = this.props;
     const inputNumberClass = classNames({
@@ -35,6 +37,14 @@ export default class InputNumber extends React.Component<InputNumberProps, any>
       [`${this.props.prefixCls}-sm`]: size === 'small',
     }, className);
 
-    return <RcInputNumber className={inputNumberClass} {...others} />;
+    return <RcInputNumber ref={c => this.inputNumberRef = c} className={inputNumberClass} {...others} />;
+  }
+
+  focus() {
+    this.inputNumberRef.focus();
+  }
+
+  blur() {
+    this.inputNumberRef.blur();
   }
 }