[flang] Fix lowering of array paths in elemental calls

Elemental procedures may need their array arguments to be passed by
address. This is done by setting ArrayExprLowering::semant to a
value that corresponds to this semantics. Later, member functions
such as applyPathToArrayLoad() read this variable to generate FIR
instructions that match the needed behavior. The problem is that
the semant variable also affects how array paths are lowered. Thus,
if an index of the path is an array element, this will cause its
address to be used instead of its value, which usually results in a
segmentation fault at runtime.

Example: b(i:i) = elem_func(a(v(i):v(i)))

To fix this, ArrayExprLowering::nextPathSemant was added. When it's
set, the next array path is handled with the semantics specified by
it, while the elemental argument retains its original semantics.

Fixes https://github.com/llvm/llvm-project/issues/62981

Reviewed By: jeanPerier

Differential Revision: https://reviews.llvm.org/D153454