AK: Make single pivot quick_sort guarantee a max stack depth of log(n)

- The change to quick_sort requires SimpleIterator to support
  assignment.
- Rename quick_sort to single_pivot_quick_sort to make it easier
  to choose a specific implementation (not based on signature).
- Ensure single_pivot_quick_sort does not copy the pivots
- Expand sorts_without_copy test case to cover both single and dual
  pivot implementations.

AK/Iterator.h

@@ -78,6 +78,13 @@ public:
     constexpr const ValueType* operator->() const { return &m_container[m_index]; }
     constexpr ValueType* operator->() { return &m_container[m_index]; }
 
+    SimpleIterator& operator=(const SimpleIterator& other)
+    {
+        m_index = other.m_index;
+        return *this;
+    }
+    SimpleIterator(const SimpleIterator& obj) = default;
+
 private:
     static constexpr SimpleIterator begin(Container& container) { return { container, 0 }; }
     static constexpr SimpleIterator end(Container& container)