[flang] Correct folding of SPREAD() for higher ranks

[klausler]

Summary

The construction of the dimension order vector used to populate the
result array was incorrect, leading to a scrambled-looking result
for rank-3 and higher results. Fix, and extend tests.

[PeteSteinfeld]

All builds and tests correctly and looks good.

flang/lib/Evaluate/fold-implementation.h

     Constant<T> spread{source->Reshape(std::move(shape))};
     std::vector<int> dimOrder;
     for (int j{0}; j < sourceRank; ++j) {
-      dimOrder.push_back(j);
+      dimOrder.push_back(j < *dim - 1 ? j : j + 1);
     }
-    dimOrder.insert(dimOrder.begin() + *dim - 1, sourceRank);
+    dimOrder.push_back(*dim - 1);
     ConstantSubscripts at{spread.lbounds()}; // all 1
     spread.CopyFrom(*source, TotalElementCount(spread.shape()), at, &dimOrder);
     return Expr<T>{std::move(spread)};

flang/test/Evaluate/fold-spread.f90

   logical, parameter :: test_stov = all(spread(1, 1, 2) == [1, 1])
   logical, parameter :: test_vtom1 = all(spread([1, 2], 1, 3) == reshape([1, 1, 1, 2, 2, 2], [3, 2]))
   logical, parameter :: test_vtom2 = all(spread([1, 2], 2, 3) == reshape([1, 2, 1, 2, 1, 2], [2, 3]))
-  logical, parameter :: test_vtom3 = all(spread([1, 2], 2, 3) == reshape([1, 2, 1, 2, 1, 2], [2, 3]))
+  logical, parameter :: test_vtom3 = all(spread([1, 2], 1, 3) == reshape([1, 1, 1, 2, 2, 2], [3, 2]))
   logical, parameter :: test_log1 = all(all(spread([.false., .true.], 1, 2), dim=2) .eqv. [.false., .false.])
   logical, parameter :: test_log2 = all(all(spread([.false., .true.], 2, 2), dim=2) .eqv. [.false., .true.])
   logical, parameter :: test_log3 = all(any(spread([.false., .true.], 1, 2), dim=2) .eqv. [.true., .true.])
   logical, parameter :: test_log4 = all(any(spread([.false., .true.], 2, 2), dim=2) .eqv. [.false., .true.])
+  logical, parameter :: test_m2toa3 = all(spread(reshape([(j,j=1,6)],[2,3]),1,4) == &
+                                          reshape([((j,k=1,4),j=1,6)],[4,2,3]))
 end module