[tautschnig]

lower_address_of_array_index rewrites &a[i] to (T*)&a + i, reusing
the pointer type of the enclosing address_of expression. For nested
arrays like int a[3][4], the inner &a[1] was given type int* (from
the outer &a[1][2]), making +1 scale by sizeof(int) = 4 instead of
sizeof(int[4]) = 16.

Fix: derive the pointer type from the array element type, so that
&a[1] gets type int(*)[4] and pointer arithmetic uses the correct
stride. When the derived type differs from the original, insert a
typecast to keep enclosing expression types consistent.

Also move lower_address_of_array_index before the pointer size map
scan so that any new pointer base types (e.g. int[4]) are registered.

The C front end rewrites addresses to byte offsets before they reach
the decision procedure, so the default configuration is not affected.
The bug affects other IR producers that keep nested index expressions
inside address_of.

Fixes #9363

Found by Jeroen Robben's specification-conformance pipeline (https://reports.robben.io/methodology/).

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