Overlap performance

[AmityWilder]

(Copied from PR 4 on anadon's repo)

• Copy element Sets to temporary arrays and ArrayLists, since they will be iterated over far more than they will be searched within the overlap method.
• Implement a bounding box for the selection and remove any elements not overlapping the bounding box from the temporary unselected element ArrayList before any further checks.
  • Use swap-removal since order doesn't matter, making the removal worst case $O(1)$ instead of $O(n)$
• Crunch the $O(n^3)$ section in the "else" case for simple intersections down to $O(n^2)$, since that part seems to just be checking against all elements per element per selected element--despite only involving the selected element and all other elements, not the selected element and all permutations of other elements.
  i.e.

for (Element sel : selected) {          // O(n)
  for (Element el : elementsArr) {      // O(n^2)
    if (intersecting) { ... }
    else {
      for (Element elm : elementsArr) { // O(n^3)
        if (sel ? elm) // no mention of `el`

$$\large\Downarrow$$

for (Element sel : selected) {       // O(n)
  for (Element el : elementsArr) {   // O(n^2)
    if (intersecting) { ... }
  }
  if (none intersected) {
    for (Element el : elementsArr) { // O(n^2)
      if (sel ? el) // ...