Add HTMLPictureElement

Fix tag mapping for various types (including Source, which is Picture related).

src/main_legacy_test.zig

@@ -38,6 +38,8 @@ pub fn main() !void {
             .user_agent_suffix = "internal-tester",
         },
     } });
+    defer config.deinit(allocator);
+
     var app = try lp.App.init(allocator, &config);
     defer app.deinit();