[RFC] Deprecate promise progress API

[clue]

This ticket serves as a basis for discussing deprecating the promise progress API.
This has come up quite a few times.

As a first step, this ticket aims to only deprecate the existing functionality and update the documentation accordingly. At a later stage, we should consider dropping the functionality altogether (BC break ahead).

Opening this ticket as an RFC and for the reference.

[jsor]

References of JS promise libraries deprecating the progression API:

• https://github.com/petkaantonov/bluebird/blob/master/API.md#progression-migration
• https://github.com/cujojs/when/blob/master/docs/api.md#promiseprogress

[jsor]

I'm planning to remove the progression API for 3.0.

[clue]

👍