AK: Add an abstraction over multiple disjoint buffers

DisjointChunks<T> provides a nice interface over multiple sequential
Vector<T>'s, allowing the user to iterate over/index into/slice from
said buffers as if they were a single contiguous buffer.
To work with views on such objects, DisjointSpans<T> is provided, which
has the same behaviour but does not own the underlying objects.

Tests/AK/CMakeLists.txt

@@ -17,6 +17,7 @@ set(AK_TEST_SOURCES
     TestCircularDuplexStream.cpp
     TestCircularQueue.cpp
     TestComplex.cpp
+    TestDisjointChunks.cpp
     TestDistinctNumeric.cpp
     TestDoublyLinkedList.cpp
     TestEndian.cpp