AK: Return early from swap() when swapping the same object

When swapping the same object, we could end up with a double-free error.
This was found while quick-sorting a Vector of Variants holding complex
types, reproduced by the new swap_same_complex_object test case.

Tests/AK/CMakeLists.txt

@@ -51,6 +51,7 @@ set(AK_TEST_SOURCES
     TestSourceLocation.cpp
     TestSpan.cpp
     TestStack.cpp
+    TestStdLibExtras.cpp
     TestString.cpp
     TestStringUtils.cpp
     TestStringView.cpp