Implement conversion from IceResult into BreadcrumbTreeNode.

I believe this change will remove an extra heap allocation I was doing in the new_breadcrumbs_* functions for the explicit context by adding support for converting from Rc<dyn ContextElement> to Rc<dyn IntoContextElement> without copying the underlying data. This should allow conversion of the IceResult::Owned variant to the BreadcrumbTreeElement::Owned variant without extra copying.

src/renderer/context_element.rs

@@ -16,6 +16,7 @@ pub trait ContextElement:
     // + CloneIntoBoxedContextElement
     + CompareContextElement
     + FromContextElement
+    + IntoRcIce
 {
 }
 
@@ -119,6 +120,16 @@ impl<C: ContextElement> IntoContextElement for C {
     }
 }
 
+pub trait IntoRcIce {
+    fn into_rc_ice(self: Rc<Self>) -> Rc<dyn IntoContextElement>;
+}
+
+impl<C: 'static + ContextElement> IntoRcIce for C {
+    fn into_rc_ice(self: Rc<C>) -> Rc<dyn IntoContextElement> {
+        Rc::clone(&self) as Rc<dyn IntoContextElement>
+    }
+}
+
 #[derive(Clone, Debug)]
 pub enum IceResult<'a> {
     // Using Rc so that when we need to create BreadcrumbTrees with