url: repeated slashes in file URL should be arranged

[watilde]

In the http scheme, the slashes after the colon are brought together in two, but it seems that it remains as it is in the file scheme.

const URL = require('url').URL

new URL('http://////example.com').href
//  =>  'http://example.com/'

new URL('file://////foo/bar').href
//  =>  'file://////foo/bar'
// it should be `file:///foo/bar`

Issue report on the spec: whatwg/url#232

[jasnell]

Will keep an eye on the whatwg/url issue. If that gets fixed upstream we will get it fixed here.

[watilde]

Spec is landed:tada:, but let's wait to start implementation till #12058 get a merge since it potentially makes some conflicts in test/src. I'm gonna work on it.