Update View Config generator to create command methods
Summary:
Flow types like this:
```
interface NativeCommands {
+hotspotUpdate: (viewRef: React.Ref<'RCTView'>, x: Int32, y: Int32) => void;
}
export const Commands = codegenNativeCommands<NativeCommands>();
```
get turned into this:
```
export const Commands = {
hotspotUpdate(viewRef: React.Ref<'RCTView'>, x: number, y: number) {
UIManager.dispatchViewCommand(
findNodeHandle(viewRef),
UIManager.getViewManagerConfig('RCTView').Commands.hotspotUpdate,
[x, y]
);
}
}
```
Reviewed By: rickhanlonii
Differential Revision: D15953126
fbshipit-source-id: edbb91056347d021dd0683391c903b76f3d1c33f