perf: speed up mapOfSubdocs benchmark by 4x by avoiding unnecessary O(n^2) loop in getPathsToValidate()

[vkarpov15]

Summary

Flame graph helped identify that most of the time was spent in the following loop. With a faster implementation that doesn't loop through all modified paths for every subdocument, Mongoose is now 3-4x faster on the mapOfSubdocs benchmark.

for (const subdoc of subdocs) {
  for (const p of paths) {
    if (p == null || p.startsWith(fullPathToSubdoc + '.')) {
      paths.delete(p);
    }
  }
}

Before this change:

{
  "Average save time ms": 439.4
}

After this change:

{
  "Average save time ms": 145.8
}

Flamegraph now looks a bunch more reasonable too:

I think we can now mark #13191 and #13271 as fixed, because $__reset() is no longer a bottleneck and between this PR and #13280 Mongoose is now more than 10x faster on this particular benchmark.

Examples

[hasezoey]

LGTM, is this only for 6.x or will this be added to 7.x too?

[vkarpov15]

We still merge everything from 6.x back into master, so this will end up in the next 7.x release too.

[Uzlopak]

LGTM
Awesome

[AbdelrahmanHafez]

Nice! LGTM, thanks! 👍