fix(Popup): fix positioning in scrollable container

[layershifter]

Fixes #1335.

Popper.JS relies on getScrollParent() function which recursively uses getParentNode() under hood. getParentNode() uses parentNode field and our ReferenceProxy doesn't have it before 😢

[codecov]

Codecov Report

Merging #1341 into master will decrease coverage by 0.02%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master    #1341      +/-   ##
==========================================
- Coverage   72.31%   72.29%   -0.03%     
==========================================
  Files         762      762              
  Lines        5765     5767       +2     
  Branches     1711     1712       +1     
==========================================
  Hits         4169     4169              
- Misses       1590     1592       +2     
  Partials        6        6

Impacted Files	Coverage Δ
...src/components/Popup/createPopperReferenceProxy.ts	38.46% <0%> (-7%)	⬇️

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[bmdalex]

👍