Change origin getter result for file: URLs to "null"

[TimothyGu]

https://url.spec.whatwg.org/#concept-url-origin says:

A URL’s origin is the origin returned by running these steps, switching on URL’s scheme:

…

"file"

Unfortunate as it is, this is left as an exercise to the reader. When in doubt, return a new opaque origin.

[TimothyGu]

whatwg-url/src/url-state-machine.js

Lines 1250 to 1252 in 4a073d8

	case "file":
	// spec says "exercise to the reader", chrome says "file://"
	return "file://";

[TimothyGu]

See also nodejs/node#21955

[domenic]

+1 on this, although it may be a major version bump since it changes the same-originness of file URLs?