feat(transformer): support for transforming legacy decorator

crates/oxc_ast/src/ast_builder_impl.rs

@@ -188,6 +188,24 @@ impl<'a> AstBuilder<'a> {
         mem::replace(function, empty_function)
     }
 
+    /// Move a class out by replacing it with an empty [`Class`].
+    pub fn move_class(self, class: &mut Class<'a>) -> Class<'a> {
+        let empty_class = self.class(
+            SPAN,
+            ClassType::ClassDeclaration,
+            self.vec(),
+            None,
+            NONE,
+            None,
+            NONE,
+            None,
+            self.class_body(SPAN, self.vec()),
+            false,
+            false,
+        );
+        mem::replace(class, empty_class)
+    }
+
     /// Move an array element out by replacing it with an [`ArrayExpressionElement::Elision`].
     pub fn move_array_expression_element(
         self,

crates/oxc_transformer/src/common/helper_loader.rs

@@ -164,6 +164,8 @@ pub enum Helper {
     ReadOnlyError,
     WriteOnlyError,
     CheckInRHS,
+    Decorate,
+    DecorateParam,
 }
 
 impl Helper {
@@ -193,6 +195,8 @@ impl Helper {
             Self::ReadOnlyError => "readOnlyError",
             Self::WriteOnlyError => "writeOnlyError",
             Self::CheckInRHS => "checkInRHS",
+            Self::Decorate => "decorate",
+            Self::DecorateParam => "decorateParam",
         }
     }
 }