AK: Implement Span which represents a contiguous sequence of objects.

This makes it possible to pass one object rather than pointer and length
individually.

AK/Vector.h

@@ -29,6 +29,7 @@
 #include <AK/Assertions.h>
 #include <AK/Forward.h>
 #include <AK/Optional.h>
+#include <AK/Span.h>
 #include <AK/StdLibExtras.h>
 #include <AK/Traits.h>
 #include <AK/kmalloc.h>
@@ -186,6 +187,9 @@ public:
         m_size = other.size();
     }
 
+    Span<T> span() { return { data(), size() }; }
+    Span<const T> span() const { return { data(), size() }; }
+
     // FIXME: What about assigning from a vector with lower inline capacity?
     Vector& operator=(Vector&& other)
     {