[fix] better flip animation

[Rich-Harris]

fixes #6657

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Tests

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[simeydotme]

This merge regresses a previous fix I submitted for animations happening inside of a scaled parent; #3627

Here's a REPL demonstrating the better flip animation failing to account for the scaled parent.
https://svelte.dev/repl/bc936592fbd24977ac21dce48e3b7e3d?version=3.42.1

The regression breaks in UIs like my scenario where I scale the <main> viewport when opening an option/editor panel.

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I will see if I can get the original fix I submitted re-applied to this new flip animation if you like? Or was the regression planned