Fix SIZEOF handling.

I have to admit that I do understand what the current code does,
but do not understand what the previous code did. However, it
still passes the testsuite - and also some code which did ICE
now compiles :-)

While writing the testcase, I did find two issues:
* Passing a CLASS to TYPE(*),dimension(..) will have an
   elem_len of the declared type and not of the dynamic type.
   https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104844
* var%class_array(1,1)%array will have size(...) == 0
   instead of size(... % array).
   https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104845

OK for mainline? (Unless you want to hold off until GCC 13)

Tobias

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