Expose slice plan (#4526)

* Expose slice plan

* Style
Co-authored-by: Scott Cyphers <diyessi@users.noreply.github.com>

src/ngraph/slice_plan.hpp

@@ -40,7 +40,7 @@ namespace ngraph
     //
     // A SlicePlan is used to collect parameters for these ops.
     //
-    struct SlicePlan
+    struct NGRAPH_API SlicePlan
     {
         // Parameters for the Slice
         std::vector<int64_t> begins;
@@ -55,7 +55,7 @@ namespace ngraph
         AxisSet reverse_axes;
     };
 
-    SlicePlan make_slice_plan(const Shape& input_shape,
+    SlicePlan NGRAPH_API make_slice_plan(const Shape& input_shape,
                                          const std::vector<int64_t>& begins,
                                          const std::vector<int64_t>& ends,
                                          const std::vector<int64_t>& strides,