Optimize browser bundle for wpapi/fetch

[kadamwhite]

Extracted from #432, we should try to alias out fetch and form-data to avoid bloating the browser build. We'd want to note to add a fetch polyfill for IE11 support, but one is built into WordPress itself.

[andrewmclagan]

This looks great. Fetch is very well supported with good isomorphic polyfils available. Superagent being somewhat bloated and redundant in-light of fetch support.

My only comment would e IE11 is currently broken anyway...?

[kadamwhite]

IE11 issue will be addressed separately :grimacing: I regret missing that one and am glad that several issues were opened catching the mistake... if anybody has bandwidth to help PR that fix, assistance would be significantly appreciated!

[andrewmclagan]

Could do later in the month

[andrewmclagan]

I would note that despite Wordpress having a fetch polyfill, allot of folks are using Wordpress as a headless CMS