fetch: support for 101 status code

[marcosc90]

This PR adds support for 101 status code responses in case we want to support it (If not just close it, I don't have a strong opinion on this).

Being honest 101 it's rarely used except for WebSockets and we use Deno.connect for that.

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I find the spec is a bit confusing regarding 1xx status codes.

Here's how it works on other browsers:

• Firefox: 101 responses work correctly
• Chrome: fetch just stays idle and never resolves
• Opera: fetch just stays idle and never resolves

In all browsers, the Response constructor fails if status === 101, the same happens in Deno.

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Deno fetch fails for all 1xx except 101 with: invalid HTTP version parsed.

[ry]

LGTM - @marcosc90 I don't have a strong opinion about this either - but given that you've done research around this I think we should go with this.