[react-native] Fix Picker component definitions + test (#42024)

* add test to show the problem

* make it work

types/react-native/index.d.ts

@@ -2994,7 +2994,7 @@ export class Picker extends React.Component<PickerProps> {
      */
     static MODE_DROPDOWN: string;
 
-    static Item: React.Component<PickerItemProps>;
+    static Item: React.ComponentType<PickerItemProps>;
 }
 
 /**

types/react-native/test/index.tsx

@@ -81,6 +81,7 @@ import {
     Modal,
     TimePickerAndroid,
     DatePickerAndroid,
+    Picker,
     ViewPropTypes,
     requireNativeComponent,
     Keyboard,
@@ -898,6 +899,13 @@ const DatePickerAndroidTest = () => {
     });
 }
 
+const PickerTest = () => (
+    <Picker mode="dropdown" selectedValue="v1" onValueChange={(val: string) => {}}>
+        <Picker.Item label="Item1" value="v1" />
+        <Picker.Item label="Item2" value="v2" />
+    </Picker>
+);
+
 class BridgedComponentTest extends React.Component {
     static propTypes = {
         jsProp: PropTypes.string.isRequired,