dom: add NamedNodeMap implementation

and create Attr type

src/dom/attribute.zig

@@ -0,0 +1,15 @@
+const std = @import("std");
+
+const parser = @import("../netsurf.zig");
+
+const Node = @import("node.zig").Node;
+const DOMException = @import("exceptions.zig").DOMException;
+
+// WEB IDL https://dom.spec.whatwg.org/#attr
+pub const Attr = struct {
+    pub const Self = parser.Attribute;
+    pub const prototype = *Node;
+    pub const mem_guarantied = true;
+
+    pub const Exception = DOMException;
+};