BREAKING(Portal): use createRef() API internally

[layershifter]

This PR continues adoption of createRef().

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BREAKING CHANGES

Will affect you only if you used the PortalInner component directly before.

PortalInner returned node previously in onMount/onUnmount callbacks. Now you should use innerRef.

Before

<PortalInner onMount={(e, data) => console.log(data.node)} />

After

const innerRef = React.createRef()

<PortalInner innerRef={innerRef} />
console.log(innerRef.current)

[codecov-io]

Codecov Report

Merging #3454 into master will decrease coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #3454      +/-   ##
==========================================
- Coverage   99.89%   99.89%   -0.01%     
==========================================
  Files         172      172              
  Lines        2827     2825       -2     
==========================================
- Hits         2824     2822       -2     
  Misses          3        3

Impacted Files	Coverage Δ
src/addons/Portal/Portal.js	100% <100%> (ø)	⬆️
src/addons/Portal/PortalInner.js	100% <100%> (ø)	⬆️

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[levithomason]

Released in [email protected].