AK: Add AKString::split_limit to split strings with a limit

This is a small change to the existing split() functionality to support
the case of splitting a string and stopping at a certain number of
tokens. This is useful for parsing e.g. key/value pairs, where the value
may contain the delimiter you're splitting on.

AK/AKString.h

@@ -109,6 +109,7 @@ public:
         return m_impl->to_uppercase();
     }
 
+    Vector<String> split_limit(char separator, int limit) const;
     Vector<String> split(char separator) const;
     String substring(int start, int length) const;