perf: various improvements to speed up saveSimple

[vkarpov15]

Summary

1. Avoid repeated deletes when calling StateMachine clear()
2. Early return in applyDefaults()
3. Skipping $__resetAtomics for primitive-only docs (similar to perf(document): speed up $__reset() in saveSimple insert case #16249)
4. Avoid unnecessary IIFE
5. Avoid hooks that are unnecessarily marked as async functions - for example, saveSubdocs exits early if there's no subdocs, we shouldn't allocate an extra promise in that case
6. Only one set in getKeysInSchemaOrder.js

Before:

{
  "Average mongoose save time ms": 2.41,
  "Average driver insertOne time ms": 1.45
}
{
  "Average mongoose save time ms": 2.09,
  "Average driver insertOne time ms": 1.4
}
{
  "Average mongoose save time ms": 2.05,
  "Average driver insertOne time ms": 1.42

After:

{
  "Average mongoose save time ms": 1.99,
  "Average driver insertOne time ms": 1.36
}
{
  "Average mongoose save time ms": 1.7,
  "Average driver insertOne time ms": 1.24
}
{
  "Average mongoose save time ms": 1.73,
  "Average driver insertOne time ms": 1.38
}

Examples

[AbdelrahmanHafez]

Nice!