[flang] Enhance show_descriptor intrinsic to avoid extra descriptor copies (#173461)

Originally, the argument to show_descriptor() intrinsic was declared
with the passing mechanism of "asBox". This resulted in `fir.load`
instruction to be emitted to pass descriptor "asBox", which resulted in
extra llvm.memcpy in LLVM IR. The current change eliminates this, so
that show_descriptor() prints information about the original descriptor,
not about its copy.

The current change modifies the passing mechanism of the argument to
show_intrinsic() to "asInquired". The lowering of show_descriptor() now
passes the reference to a descriptor directly to the runtime routine. If
descriptor is passed as a value in SSA register, then it's spilled on
the stack and its address is passed to the runtime routine. If a
non-descriptor value is passed to show_descriptor(), then this value is
spilled to the stack, wrapped into a descriptor that is also spilled to
the stack, and the resulting descriptor pointer is passed to
show_descriptor().

show_descriptor() LIT test was modified to correspond to the new
implementation and additional test cases were added to it.