Previously the code was computing a prefix sum over the number of
preceding elements in tree order to get the index that the node should
be inserted in.
That's not great if the DOM tree is big. Instead, we can compare two
nodes individually by looking at their ancestor chain and then find the
correct position with binary search.
On https://262.ecma-international.org/16.0/index.html, this reduces the
time it takes for content to appear from around 33s to 16s.
Part of https://github.com/servo/servo/issues/44113
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Signed-off-by: Simon Wülker <simon.wuelker@arcor.de>
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