Instead of calling quick_sort() every time a StackingContext child
is added to a parent, we now do a single pass of sorting work after the
full StackingContext tree has been built.
Before this change, the quick_sort() was ~13.5% of the profile while
hovering links on GitHub in the Browser. After the change, it's down to
~0.6%. Pretty good! :^)
SPDX License Identifiers are a more compact / standardized
way of representing file license information.
See: https://spdx.dev/resources/use/#identifiers
This was done with the `ambr` search and replace tool.
ambr --no-parent-ignore --key-from-file --rep-from-file key.txt rep.txt *
