Stabilize k6/experimental/timers into k6/timers

[mstoykov]

What?

Stabilize k6/experimental/timers

Why?

SetTimeout and co. are basic tools needed to write most asynchronous code in javascript.

They are well known and used for years. As such having them in k6 is necessity.

They are currently under k6/timers and not available globally, but later PRs will likely also make them available globally while leaving the package versions as well and potentially adding other functions there.

see https://nodejs.org/api/timers.html or https://deno.land/std@0.110.0/node/timers.ts

Checklist

• I have performed a self-review of my code.
• I have added tests for my changes.
• I have run linter locally (make 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)

closes #3297