dom: refacto html collection to handle root or descendant only

HTMLCollection works on two different way:
* by default it must walk over root's descendants only
* on document, since the given root must be included in the walk.

src/dom/document.zig

@@ -110,6 +110,7 @@ pub const Document = struct {
             alloc,
             parser.elementToNode(root),
             tag_name,
+            true,
         );
     }
 
@@ -123,6 +124,7 @@ pub const Document = struct {
             alloc,
             parser.elementToNode(root),
             classNames,
+            true,
         );
     }