fix: send an event-like object into Field onChange when no event (#4548)

[dereksandkamp]

The docs mention that it is possible for an input to call input.onChange and pass either an event or a new value as the argument.

They also mention that it's possible to pass onChange to a <Field /> component, and that handler should receive an event as its first argument, with a preventDefault method on it which will prevent the change from being dispatched.

It's not explained in the docs that there's any connection between these two APIs. However, since this change, the consumer only receives an event object in Field.onChange if the underlying input has called input.onChange with an event.

Since many people (including myself) have been relying on the ability to BOTH pass a value to input.onChange and call event.preventDefault() within the Field.onChange handler, I think we should either make that possible or update the docs to explain the restriction. This PR makes it possible.

Closes #4548

[codecov-io]

Codecov Report

Merging #4604 into master will not change coverage.
The diff coverage is 87.5%.

@@           Coverage Diff           @@
##           master    #4604   +/-   ##
=======================================
  Coverage   99.42%   99.42%           
=======================================
  Files          74       74           
  Lines        1745     1745           
=======================================
  Hits         1735     1735           
  Misses         10       10

Impacted Files	Coverage Δ
src/ConnectedField.js	95.45% <87.5%> (ø)	⬆️

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[machinek56]

Hi guys! Any updates on this PR?
@dereksandkamp @iamandrewluca

[iamandrewluca]

I'll try to find some time this week to review this. From what I saw it seems this may be a breaking change.
Implicated in some urgent COVID-19 projects and don't have to much time to allocate for redux-form

[dereksandkamp]

Thanks! For what is worth, from my perspective the breaking change already happened and this is a fixing change 😆

[machinek56]

@dereksandkamp, for now i wrapped your PR into own package as we extremely need it.

[duyenho]

👋 @iamandrewluca and @dereksandkamp
cc: @machinek56

Hope everyone is safe during COVID-19.
Would love to get this one in as well 🙂