Implement the size helper but it has a bug somewhere.

src/renderer/renderer.rs

@@ -723,8 +723,21 @@ impl<'a> DustRenderer<'a> {
                 }
             }
             DustTag::DTHelperSize(parameterized_block) => {
-                //todo
-                todo!()
+                let param_map =
+                    ParametersContext::new(self, breadcrumbs, &parameterized_block.params, None);
+                let value = self.tap(breadcrumbs, &param_map, "key");
+                let value_ce = value.as_ref().map(|maybe_ice| {
+                    maybe_ice
+                        .as_ref()
+                        .map(|ice| ice.get_context_element_reference())
+                        .map(|ce| ce.get_size())
+                });
+                match value_ce {
+                    None | Some(Err(_)) | Some(Ok(None)) => return Ok("".to_owned()),
+                    Some(Ok(Some(ce_size))) => {
+                        return ce_size.get_context_element_reference().render(&Vec::new())
+                    }
+                }
             }
             DustTag::DTHelperContextDump(parameterized_block) => {
                 //todo