fix: invoke mapNodesToParents lazily

[SethFalco]

In a recent PR, I introduced a significant performance regression to SVGO. This was missed as it only had a noticeable impact on very large SVGs. In the SVG from #2075, it took 70~ seconds to optimize before the commit, then 240~ seconds after the commit.

This fix takes it down to around 74~ seconds on my machine.

Instead of populating the map of nodes to parent nodes eagerly when creating the css-select Adapter, we now defer it to when css-select would actually invoke the Adapter#getParent method. In most instances, the map was never being used, so it was a waste of compute to initialize and populate the map.

To avoid Rollup reporting circular dependencies, I've created a util directory, and migrated some of the helpers to isolated files.

Related

• Issue introduced in chore: drop parentNode property #2113
• SVG tested was from Crash on svg optimization #2075