call onValueChange only when value changes (#24653)

Summary:
`OnValueChange` function of `Picker` is called when Picker is initialized.

[Android][fixed] - `OnValueChange` will be called only when the `selectedValue` changes.
Pull Request resolved: #24653

Differential Revision: D15146483

Pulled By: cpojer

fbshipit-source-id: e26f5aa4caa673015c50c853f00b99572e803755

Libraries/Components/Picker/PickerAndroid.android.js

@@ -119,7 +119,9 @@ class PickerAndroid extends React.Component<
         const value = children[position].props.value;
         /* $FlowFixMe(>=0.78.0 site=react_native_android_fb) This issue was
          * found when making Flow check .android.js files. */
-        this.props.onValueChange(value, position);
+        if (this.props.selectedValue !== value) {
+          this.props.onValueChange(value, position);
+        }
       } else {
         this.props.onValueChange(null, position);
       }