Add new URL(someUrl, undefined) feature testing for URL polyfill

[trotyl]

From URL specification, the URL constructor has an optional base parameter:

interface URL {
  constructor(USVString url, optional USVString base);
};

From Web IDL spec, explicit passed undefined is treated as missing value:

In the ECMAScript binding, a value of undefined is treated as not present, or will trigger the default value where applicable.

So that new URL(text, undefined) should be equivalent to new URL(text), but which failed in Safari (tested in 13.0.1) by throwing a TypeError:

This should be a BUG in JavaScriptCore implementation, where in Chrome and Firefox it works properly:

Currently the native-url testing cannot detect this failure and may resulting a malfunctioning Safari native URL being used even when this polyfill loaded.

[zloirock]

native-url test relaxed because at the moment of writing core-js URL polyfill no one from browsers implementations were enough correct by the spec at least in some aspects. However, I think makes sense to make it a little more strict at least at this moment.

[dilyanpalauzov]

Filed https://bugs.webkit.org/show_bug.cgi?id=216841 for new URL('https://x', undefined) throwing an error in WebKit.

[dilyanpalauzov]

Which test fails on Safari for URLSearchParams, so that 8699b9a#diff-6016a0a7725ceb1f68ed6ea1c7b96491 requires polyfill only for it?