LibURL/Pattern: Add a representation of a URL Pattern

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.

Libraries/LibURL/CMakeLists.txt

@@ -7,6 +7,7 @@ set(SOURCES
     Site.cpp
     URL.cpp
     ${PUBLIC_SUFFIX_SOURCES}
+    Pattern/Pattern.cpp
 )
 
 serenity_lib(LibURL url)