AK: Add a new, spec-compliant URLParser

This adds a new URL parser, which aims to be compliant with the URL
specification (https://url.spec.whatwg.org/). It also contains a
rudimentary data URL parser.

AK/URL.h

@@ -15,6 +15,8 @@ namespace AK {
 // NOTE: The member variables cannot contain any percent encoded sequences.
 //       The URL parser automatically decodes those sequences and the the serialize() method will re-encode them as necessary.
 class URL {
+    friend class URLParser;
+
 public:
     enum class PercentEncodeSet {
         C0Control,