Address eventloop's double registerCallback call when using promises.New

[oleiade]

What?

This Pull Request addresses the misuse of named arguments introduced by #3176, and fixes the resulting registerCallback called twice issue that followed from it.

It also adds two minimal tests covering ensuring the resolve and reject callbacks are effective. I wasn't entirely sure how to properly test that function; this is the simplest thing I came up with. I'm all ears 👂🏻 for alternatives and suggestions to improve it 🙇🏻

Why?

As I started using the promises.New function in another stream of work, I noticed that as soon as I used the promises.New function, I would end up having registerCallback called twice panic all over. I tracked down the issue, and it turned out that it was because we needed to use Go named return arguments properly.

Checklist

• I have performed a self-review of my code.
• I have added tests for my changes.
• I have run linter locally (make ci-like-lint) and all checks pass.
• I have run tests locally (make tests) and all tests pass.
• I have commented on my code, particularly in hard-to-understand areas.

Related PR(s)/Issue(s)

ref #3176
ref #3176 (review)

[codecov-commenter]

Codecov Report

Merging #3180 (5d5e15b) into master (3906dcf) will increase coverage by 0.02%.
The diff coverage is 100.00%.

❗ Current head 5d5e15b differs from pull request most recent head 75c8d47. Consider uploading reports for the commit 75c8d47 to get more accurate results

@@            Coverage Diff             @@
##           master    #3180      +/-   ##
==========================================
+ Coverage   72.77%   72.80%   +0.02%     
==========================================
  Files         255      256       +1     
  Lines       19686    19697      +11     
==========================================
+ Hits        14327    14340      +13     
+ Misses       4463     4462       -1     
+ Partials      896      895       -1     

Flag	Coverage Δ
ubuntu	72.73% <100.00%> (+0.02%)	⬆️
windows	72.64% <100.00%> (+0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
js/promises/promises.go	100.00% <100.00%> (ø)

... and 1 file with indirect coverage changes

[mstoykov]

So for future reference - the problem here was that resolve here is the same resolve we return - which is the function we in. So this just recurse inside itself.