URLPattern: Apply syntax changes from whatwg/urlpattern#179.

The following changes apply to patterns which are constructed
using a base URL, the string syntax, or both -- but not any
pattern which explicitly specifies components separately without
a base URL.

* Components are not inherited from a base URL if an "earlier"
  component is explicitly specified.
* In the string format, unspecified "later" components are
  implicitly wildcarded, rather than required to be empty
  (with the exception of the port, which is always taken to
  be specified when the hostname is).
* Username and password are never implicitly specified or
  inherited.

This means that a pattern like "https://example.com/*" also
matches with any username, password, search, and hash.
Previously this would be written
"https://*:*@example.com/*\\?*#*".

Bug: 1468446
Change-Id: Ie0d7a80e36e89e05a0c634f7565c3365909edb2d