Fixing ProgressEvent type definitions so that Axios doesn't have to depend on lib dom (Fixes #3219)

[jan-molak]

As noted in #3219, Axios 0.20.0 introduced an implicit dependency on lib dom, which prevents transpilation of pure Node.js projects using Axios (such as Serenity/JS REST).

Instead of making the dependency semi-explicit, as per the suggestion in #3221, I'd like to propose to avoid the dependency altogether by replacing ProgeressEvent type with its structural equivalent:

{ lengthComputable?: boolean; loaded?: number; total?: number }

This change will allow Axios (and any other project using, for that matter) to avoid having to depend on lib dom while still providing type information better than using any.

[sk-]

Thanks @jan-molak, I think it's much better now.

Let's see what the maintainers think about it.

@jasonsaayman any chance to review this PR?

[chinesedfan]

Closed in favor of #3237 (comment). Thanks for your contribution all the same.