[JS] Use iterators instead of generators in critical code paths

[asfimport]

I found that generators are generally slower than iterators in most browsers. See https://observablehq.com/@domoritz/yield-vs-iterator-vs-callback. I attached the results for Chrome. We should consider using iterators instead of generators for iterating over row proxies and vectors. 

Reporter: Dominik Moritz / @domoritz
Assignee: Dominik Moritz / @domoritz

Original Issue Attachments:

• Screen Shot 2021-04-08 at 09.40.51.png

PRs and other links:

• GitHub Pull Request #9962

_{Note: This issue was originally created as ARROW-12303. Please see the migration documentation for further details.}

[asfimport]

Neal Richardson / @nealrichardson:
Issue resolved by pull request 9962
#9962