new method on core Expr (#1428)

Signed-off-by: Craig Disselkoen <cdiss@amazon.com>

cedar-policy-core/src/ast/expr.rs

@@ -222,6 +222,12 @@ impl<T> Expr<T> {
         self.data
     }
 
+    /// Consume the `Expr`, returning the `ExprKind`, `source_loc`, and stored
+    /// data.
+    pub fn into_parts(self) -> (ExprKind<T>, Option<Loc>, T) {
+        (self.expr_kind, self.source_loc, self.data)
+    }
+
     /// Access the `Loc` stored on the `Expr`.
     pub fn source_loc(&self) -> Option<&Loc> {
         self.source_loc.as_ref()
@@ -1455,10 +1461,9 @@ impl<T: Default + Clone> expr_builder::ExprBuilder for ExprBuilder<T> {
 }
 
 impl<T> ExprBuilder<T> {
-    /// Internally used by the following methods to construct an `Expr`
-    /// containing the `data` and `source_loc` in this `ExprBuilder` with some
-    /// inner `ExprKind`.
-    fn with_expr_kind(self, expr_kind: ExprKind<T>) -> Expr<T> {
+    /// Construct an `Expr` containing the `data` and `source_loc` in this
+    /// `ExprBuilder` and the given `ExprKind`.
+    pub fn with_expr_kind(self, expr_kind: ExprKind<T>) -> Expr<T> {
         Expr::new(expr_kind, self.source_loc, self.data)
     }