don't run `e.persist()` in `_onFocus()` when customInput doesn't have attribute `.persist()`

[corsin-ragettli]

Describe the issue and the actual behavior

I have a type issue when I input a custom component in NumericFormat because e.persist() doesn't exist on my component when onFocus is called.

Describe the expected behavior

NumericFormat doesn't call e.persist() when component is focused

Please check the browsers where the issue is seen

• Chrome
• Chrome (Android)
• Safari (OSX)
• Safari (iOS)
• Firefox
• Firefox (Android)

[s-yadav]

Fixed on v5.1.2