<Controller> with onFocus erroneously reregisters itself

[donocode]

Describe the bug
When using a component with an onFocus callback it reregisters itself after validation failure (or if focused in react dev tools)

To Reproduce
Steps to reproduce the behavior:

1. Go to codesandbox link
2. Type some text in FirstName and click submit (don't add text to LastName)
3. See how the FirstName was reset
4. See how you can no longer type in FirstName

Codesandbox link (Required)

https://codesandbox.io/s/controller-issue-6gr5t?file=/src/index.js

Expected behavior
Having an onFocus callback should not cause the input to reregister on validation failure

Screenshots
If applicable, add screenshots to help explain your problem.

Desktop (please complete the following information):

• OS: OSX High Sierra
• Browser: Chrome
• Version: 81.0.4044.113

Additional context
The reregistering problem will also occur if you focus the Controller in react dev tools. If you have multiple Controllers in the form with onFocus callbacks then they will all exhibit the same behaviour

[JeromeDeLeon]

The reason for this is because your forgot to memoize your function.

In Line 107 of Controller, notice that the onFocus is part of useCallback's dependencies of registerField hence re-register happen because onFocus handler is creating new reference for every render.

[JeromeDeLeon]

@bluebill1049, should we handle it inside or let user defines it?

[bluebill1049]

wow, awesome find! @JeromeDeLeon it's awesome to see you are taking over the Controller component! I think we should memo in the lib.