add padding field for some other webapi

src/browser/webapi/DOMParser.zig

@@ -29,6 +29,9 @@ const Document = @import("Document.zig");
 
 const DOMParser = @This();
 
+// Padding to avoid zero-size struct, which causes identity_map pointer collisions.
+_pad: bool = false,
+
 pub fn init() DOMParser {
     return .{};
 }

src/browser/webapi/ResizeObserver.zig

@@ -22,6 +22,9 @@ const Element = @import("Element.zig");
 
 pub const ResizeObserver = @This();
 
+// Padding to avoid zero-size struct, which causes identity_map pointer collisions.
+_pad: bool = false,
+
 fn init(cbk: js.Function) ResizeObserver {
     _ = cbk;
     return .{};

src/browser/webapi/XMLSerializer.zig

@@ -25,6 +25,9 @@ const dump = @import("../dump.zig");
 
 const XMLSerializer = @This();
 
+// Padding to avoid zero-size struct, which causes identity_map pointer collisions.
+_pad: bool = false,
+
 pub fn init() XMLSerializer {
     return .{};
 }