This is the core object behind a URL pattern which when constructed
can be used for matching the pattern against URLs.
However, the implementation here is missing key functions such as
the constructor and the 'test'/'exec' functions as that relies on
a significant amount of supporting URLPattern infrastructure such
as two different parsers and a tokenizer.
However, this is enough for us to implement some more of the IDL
wrapper layer of this specification.
This is the return value of a URLPattern after `exec` is called on it.
It conveys information about the named (or unammed) regex groups
matched for each component of the URL. For example,
```
let p = new URLPattern({ hostname: "{:subdomain.}*example.com" });
const result = pattern.exec({ hostname: "foo.bar.example.com" });
console.log(result.hostname.groups.subdomain);
```
Will log 'foo.bar'.
The URLPattern spec is intended to be implemented inside of LibURL, with
LibWeb only responsible for the IDL conversion layer, in a similar
manner to how URL is implemented.
