useMergedState.ts

[GuichiZhao]

In triggerChange function, why not ignore setInnerValue when value present, i.e. controlled mode. I suppose innerValue does not take any effect in controlled mode though.

In addition, it should be nice to add some logic detecting the switch controlled and uncontrolled mode, throw an error/warning as native react dose facebook/react#5821.

Not sure if I am missing some points though, if the above idea make any sense. I am glad to implement the code