[MLIR][Affine] Expose getAffineScope as a utility function

[wsmoses]

Summary

The getAffineScope function is currently internal
to AffineOps.cpp. However, as the comment on the function
itself notes, this is useful in a variety of other places
externally. This PR allows other files to use the function.

[wsmoses]

Fix format

[wsmoses]

Fix build

mlir/include/mlir/Dialect/Affine/IR/AffineOps.h

 class AffineValueMap;
 
 /// A utility function to check if a value is defined at the top level of an
 /// op with trait `AffineScope` or is a region argument for such an op. A value
 /// of index type defined at the top level is always a valid symbol for all its
 /// uses.
 bool isTopLevelValue(Value value);
 
+/// Returns the closest region enclosing `op` that is held by an operation with
+/// trait `AffineScope`; `nullptr` if there is no such region.
+Region *getAffineScope(Operation *op);
+
 /// AffineDmaStartOp starts a non-blocking DMA operation that transfers data
 /// from a source memref to a destination memref. The source and destination
 /// memref need not be of the same dimensionality, but need to have the same
 /// elemental type. The operands include the source and destination memref's
 /// each followed by its indices, size of the data transfer in terms of the
 /// number of elements (of the elemental type of the memref), a tag memref with
 /// its indices, and optionally at the end, a stride and a
 /// number_of_elements_per_stride arguments. The tag location is used by an

mlir/lib/Dialect/Affine/IR/AffineOps.cpp

bool mlir::isTopLevelValue(Value value) {
   }
   // The defining Op may live in an unlinked block so its parent Op may be null.
   Operation *parentOp = value.getDefiningOp()->getParentOp();
   return parentOp && parentOp->hasTrait<OpTrait::AffineScope>();
 }
 
 /// Returns the closest region enclosing `op` that is held by an operation with
 /// trait `AffineScope`; `nullptr` if there is no such region.
-//  TODO: getAffineScope should be publicly exposed for affine passes/utilities.
-static Region *getAffineScope(Operation *op) {
+Region *mlir::getAffineScope(Operation *op) {
   auto *curOp = op;
   while (auto *parentOp = curOp->getParentOp()) {
     if (parentOp->hasTrait<OpTrait::AffineScope>())
       return curOp->getParentRegion();
     curOp = parentOp;
   }
   return nullptr;
 }