fix(Flex): FlexProps extends UIComponentProps

[miroslavstastny]

FlexProps now extends UIComponentProps.
Fixes #1078

[codecov]

Codecov Report

Merging #1089 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master    #1089   +/-   ##
=======================================
  Coverage   82.09%   82.09%           
=======================================
  Files         717      717           
  Lines        8567     8567           
  Branches     1167     1167           
=======================================
  Hits         7033     7033           
  Misses       1518     1518           
  Partials       16       16

Impacted Files	Coverage Δ
packages/react/src/components/Flex/FlexItem.tsx	87.5% <100%> (ø)	⬆️
packages/react/src/components/Flex/Flex.tsx	100% <100%> (ø)	⬆️

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