Previously we were inconsistent by generating code for enum definitions
but not generating code for dictionaries. With future changes to the
IDL generator to expose helpers to convert to and from IDL values
this produced circular depdendencies. To solve this problem, also
generate the dictionary definitions in bindings headers.
This is to save a future name conflict that will appear between
the options IDL dictionary and the options struct that are both
present in the spec.
It is also a nicer interface for now given there is only a single
option at the moment.
There is further work needed to complete the implementation of
URL::Pattern::Pattern, but this implements the remaining URLPattern
exec and test IDL interfaces, leaving all remaining work to LibURL.
