Handle SkipDefaultValuesSerializationFilters param deprecation

[juan-mora-google]

Changes

The override of the writeExternal method was using XmlSerializer.serializeInto, with 3 params, included a new instance of SkipDefaultValuesSerializationFilters which was recently deprecated.

Faster and less disruptive solution was moving from XmlSerializer.serializeInto to XmlSerializer.serialize with just one param, preventing refactors that could potentially break clone() and getParameters() methods.

XmlSerializer.serialize(Object) automatically ignores default and null values, this means it replaces the old work done by SkipDefaultValuesSerializationFilters.

Why was this needed?

JetBrains declared this as deprecated because direct mutation of existing DOM elements causes problems with the modern state system.

---

• I’ve reviewed the contributor guide and applied the relevant portions to this PR.

Contribution guidelines:

• See our [contributor guide](https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md for general expectations for PRs.
• Larger or significant changes should be discussed in an issue before creating a PR.
• Dart contributions to our repos should follow the Dart style guide and use dart format.
• Java and Kotlin contributions should strive to follow Java and Kotlin best practices (discussion).

[google-cla]

Thanks for your pull request! It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

View this failed invocation of the CLA check for more information.

For the most up to date status, view the checks section at the bottom of the pull request.

[gemini-code-assist]

Code Review

This pull request updates the serialization logic in DartWebdevConfiguration.java by replacing the deprecated SkipDefaultValuesSerializationFilters with manual serialization and copying of attributes. It also fixes a minor typo in a comment. The reviewer suggests using SkipDefaultsSerializationFilter as a direct, non-deprecated replacement to maintain clean, single-line serialization and avoid manual DOM manipulation.