perf: improve validation sync and async by replacing forEach with classic for loops

[Uzlopak]

It is basically replacing the forEach with classic for loop

before

MONGOOSE_DEV=1 node validate
invalid x 23,482 ops/sec ±3.63% (89 runs sampled)
valid x 75,238 ops/sec ±0.58% (91 runs sampled)

after

MONGOOSE_DEV=1 node validate
invalid x 27,460 ops/sec ±0.91% (89 runs sampled)
valid x 76,128 ops/sec ±0.69% (93 runs sampled)

[Uzlopak]

why do we need to keep track if we are validated a path already?

[vkarpov15]

I don't recall exactly, but it has something to do with subdocuments or nested paths. Having both the parent path and child path modified at the same time can cause double validation.

[AbdelrahmanHafez]

God bless unit tests.
In an ideal world, we can not do that and see what test fails.