Perf improvements when creating arrays of primitives

[vkarpov15]

Summary

Re: #11380, #13546. This one quick improvement of using push() instead of concat() already helps shave off maybe 10% off of #11380.

Before:

l100.avg=1140.53, total.avg=3175.7342

After:

l100.avg=1249.86, total.avg=2870.4085

Gonna work to see what other performance wins we can turn up.

Examples

[vkarpov15]

With 7d26ad2 we've managed to shave off a total of 40%:

l100.avg=1117, total.avg=1898.9985

vs latest 7.x:

l100.avg=1116.11, total.avg=3078.2941

Mongoose 7.x is now significantly faster (about 35%) than latest Mongoose 4 at pushing elements onto an array:

l100.avg=492.34, total.avg=2761.561

[vkarpov15]

New flamegraph:

[hasezoey]

Looks good to me, but i am not quite sure what actually changed or performance characteristics (it seems like setters are called less?)