This provides the infrastructure for taking a part list from the
pattern parser and generating the actual regexp object which is
used for matching against URLs from the pattern.
These control how a pattern string is generated, which can vary for
different components and is also impacted by the 'ignoreCase' option
that can be provided in the URLPattern constructor.
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.
A URL pattern consists of components such as the 'port', 'password'
'hostname', etc. A component is compiled from the input to the
URLPattern constructor and is what is used for matching against
URLs to produce a match result.
This is also where the regex dependency is introduced into LibURL
to support the URLPattern implementation.
This lets us move a few Host-related functions (like serialization and
checks for what the Host is) into Host instead of having them dotted
around the codebase.
For now, the interface is still very Variant-like, to avoid having to
change quite so much in one go.
