Add aligned_accessor example

1. aligned_accessor uses compiler identification macros to pick
   from various, possibly nonstandard ways to mark a pointer
   (its value, and/or its type) as having a specific alignment.

2. "Aligned" benchmarks use overaligned allocation
   and the aforementioned way to mark a pointer as aligned.

3. "Unaligned' benchmarks access memory aligned only
   to the element type, by adding 1 (sizeof(ElementType) bytes)
   to the array start.

examples/CMakeLists.txt

@@ -15,3 +15,4 @@ add_subdirectory(godbolt_starter)
 add_subdirectory(dot_product)
 add_subdirectory(tiled_layout)
 add_subdirectory(restrict_accessor)
+add_subdirectory(aligned_accessor)

examples/aligned_accessor/CMakeLists.txt

@@ -0,0 +1 @@
+mdspan_add_example(aligned_accessor)