[Flang][OpenMP] Skip DSA for canonical loops (#150593)
OpenMP loop transformations to not have data-sharing attributes and do
not explicitly privatize the loop variable. The DataSharingProcessor was
still used in #144785 because `createAndSetPrivatizedLoopVar` expected
it.
We skip that function and directly write to the loop variable. If the
loop variable is implicitly or explicitly privatized, it will be due to
surrounding OpenMP constructs such as `parallel`.
