Form Data "files" is not correctly handled with default fetch template

[omarmciver]

Form Data "files" is not correctly handled as an array of objects in fetch templates and is inconsistent with the axios templates. As a result, an array of files in FormData are sent in the fetch POST as an empty array.

[omarmciver]

#555

[omarmciver]

@js2me First attempt at contribution. Appreciate any feedback on issue and PR submission.

[sflanker]

I think this is essentially the same issue as #462, but it's not clear why @smorimoto closed the PR #555 without comment as I think that would have fixed this.

[omarmciver]

I added a new PR #1431