fix(cli/web/fetch): Make Response constructor standard

[marcosc90]

Fixes #4667 #4748

• Remove duplicated Body implementation
• Make constructor follow the spec (see notes regarding type)
• res.body is now a ReadableStream

All tests are passing without modification, only removed a single test that was testing the previous Response constructor.

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I'm not sure about response.type

• How are basic, 'error' types set? In the previous implementation we weren't setting them either, so don't think this is a blocker right now.

Used a WeakMap to avoid adding extra settings to ResponseInit to be spec-compliant. I could use symbols instead, so please let me know.

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Any comments or improvements are welcomed.

[marcosc90]

Currently, this is most likely a breaking change. Although I'd like to modify Deno.copy to accept a ReadableStream too, so the following code will still work fine.

  const res = await fetch("http://example.com/file.bin");
  const file = await Deno.open("/tmp/file.bin", { create: true, write: true });

  await Deno.copy(res.body, file);
  file.close();

I'll submit the changes in a different PR.

[kitsonk]

LGTM

[ry]

@marcosc90 could you please merge with master?

[ry]

LGTM - thanks @marcosc90