feat(time): Add Interval class

[nkomonen-amazon]

Creates our own version of an Interval, similar to how we have our own Timeout

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License: I confirm that my contribution is made under the terms of the Apache 2.0 license.

[github-actions]

This pull request implements a feature or fix, so it must include a changelog entry. See CONTRIBUTING.md#changelog for instructions.

[hayemaxi]

QQ: How are these classes different from globals.clock.setInterval and globals.clock.setTimeout?

[nkomonen-amazon]

@hayemaxi it behaves the same, but gives us some extra control and allows us to add features to it.

An example is this nextCompletion() method which is not available ootb with globals.clock.setInterval.

It can also be thought of as how we wrap globalState or setContext

[justinmk3]

This new Interval class doesn't have a docstring, so I assume the only difference vs Timeout is that it repeats. Why can't that simply be a feature added to Timeout (if it doesn't already exist)?

[nkomonen-amazon]

@justinmk3 most of the methods in Timeout dont make sense in the context of an Interval:

• remainingTime, intervals run infinitely
• completed, intervals run infinitely
• refresh, intervals automatically refresh
• promisify, you don't wait for an interval to complete
• cancellationToken, it doesn't timeout by default

Over time if we see a use for something like elapsedTime, we could look to generalize that between Timeout and Interval

[justinmk3]

remainingTime, intervals run infinitely
completed, intervals run infinitely

That can be optional. Not an inherent property of either (except how "Interval" is currently defined in this PR).

• refresh, intervals automatically refresh

That is optional. And a caller may want to do an "eager" refresh.

• promisify, you don't wait for an interval to complete
• cancellationToken, it doesn't timeout by default

I don't understand these. But perhaps they also make sense as optional features of Timeout with "interval behavior".