Fix #3555 ; scale elements in FLIP animations

[simeydotme]

Changes

• divide the getBoundingClientRect dimensions by clientHeight or clientWidth
  • this gives us the element's scaled values as scaleX and scaleY
• divide the "dx" and "dy" by the "scaleX" and "scaleY"

This aims to fix #3555 by using the node's un-scaled width/height to
calculate the amount it has been scaled. Then dividing the distance by
this scale factor removes the janky start position which was shown in
the test case.

• repl before fix
• repl after fix

resolves #3555

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Tests

• Run the tests tests with npm test or yarn test)

[Rich-Harris]

Apologies for the delay — thank you, this is a great fix