Add missing imports

Author: MilesCranmer

src/DynamicExpressions.jl

@@ -11,9 +11,10 @@ include("SimplifyEquation.jl")
 include("OperatorEnumConstruction.jl")
 
 using Reexport
-@reexport import .EquationModule: Node, string_tree, copy_node, set_node!
+@reexport import .EquationModule: Node, string_tree, print_tree, copy_node, set_node!
 @reexport import .EquationUtilsModule:
     count_nodes,
+    count_constants,
     count_depth,
     NodeIndex,
     index_constants,
@@ -27,5 +28,6 @@ using Reexport
 @reexport import .EvaluateEquationDerivativeModule:
     eval_diff_tree_array, eval_grad_tree_array
 @reexport import .InterfaceSymbolicUtilsModule: node_to_symbolic, symbolic_to_node
+@reexport import .SimplifyEquationModule: combine_operators, simplify_tree
 
 end