fix(Body.body): Normalize Body.body into a node:stream

[jimmywarting]

Purpose

Normalize Body.body into a stream to be more in line with spec.
and also to simplify other parts so we deal with less underlying types of bodies

Changes

Constructing a Response or Request with a string, blob or anything else gets converted into a node:stream now

Previously, what you passed into the Response or Request as a body would in the end be the same thing in Body.body (new Response('abc').body === 'abc' ). This is wrong.

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• I updated ./docs/CHANGELOG.md with a link to this PR or Issue
• I added unit test(s)

Additional

Right now it's converted into a node:stream but i'm thinking it can be converted to a whatwg:stream in v4
it would be suppressing to me if someone rely on Response.body being whatever was passed to the Response constructor, not necessarily a stream. so perhaps this can slip in as a non major change?

I also lowercased the nodefetchformdataboundary cuz one issue is that Blob's type is casted to lowercase also

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• fixes #210
• fixes #1092
• fixes #1091

[LinusU]

Neat! 👍