Change URL.port implementation to match WHATWG specifications (#4954)

Changed `URL.port` implementation to match [WHATWG
specifications](https://url.spec.whatwg.org/#port-state).

This PR matches the behaviour of other browsers:

1.  a `TypeError` must be thrown when passing an URL with an invalid
port to the constructor.

2. When setting an invalid port, using property setter, I haven't found
what should happen in this case, so I mimic **Firefox** & **Node**
behaviour. If an invalid port is set, it will use the previous value.
**Chrome** sets the value to `'0'` if an invalid port is set. I prefer
to keep the previous valid value.  (I can use Chrome's behaviour if you
think it's better, it's a simple value change)

```
url.port = '3000'; // valid
url.port = 'deno'; // invalid
assertEquals(url.port, '3000');
```

3. If the port value equals the current protocol default port value,
`port` will be an empty string.

0 files changed, 0 insertions, 0 deletions