node: add lookupPrefix method (NOT TESTED)

Signed-off-by: Francis Bouvier <francis.bouvier@gmail.com>

src/dom/node.zig

@@ -175,6 +175,11 @@ pub const Node = struct {
         return parser.nodeIsSameNode(self, other);
     }
 
+    pub fn _lookupPrefix(self: *parser.Node, namespace: ?[]const u8) ?[]const u8 {
+        // TODO: other is not an optional parameter, but can be null.
+        return parser.nodeLookupPrefix(self, namespace);
+    }
+
     pub fn _normalize(self: *parser.Node) void {
         return parser.nodeNormalize(self);
     }