Auto merge of #29894 - mrobinson:ditch-static-position-closure, r=Loirooriol

Simplify layout of absolutes with static insets

Absolutes with static insets need to be laid out at their ancestor containing blocks, but their position is dependent on their parent's layout. The static layout position is passed up the tree during hoisting and ancestors each add their own offset to the position until it is relative to the containing block that contains the absolute.

This is currently done with a closure and a fairly tricky "tree rank" numbering system that needs to be threaded through the entire layout. This change replaces that system.

Every time a child is laid out we create a positioning context to hold any absolute children (this can be optimized away at a later time). At each of these moments, we call a method to aggregate offsets to the static insets of hoisted absolutes. This makes the logic easier to follow and will also allow implementing this behavior for inline-blocks, which was impossible with the old system.

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