Replace libxmljs2 with libxmljs as its no longer maintained

## Is your feature request related to a problem? Please describe.

Currently `libxmljs2` is defined as an `optionalDependency` inside `package.json`.
Since the dependency is no longer maintained and only has supply chain risks due to native code being executed on `postinstall` hooks I recommend to replace it with the original now maintained `libxmljs`

See https://socket.dev/npm/package/libxmljs2

## Describe the solution you'd like

Replace dependency in`package.json` and and fix references in `demo` and `test`.

## Additional context

## Contribution

- [x] I am willing to provide an implementation
- [ ] I will wait until somebody else implements it

Start in package.json, then search the demo and test directories for libxmljs2 references and review the existing dependency-related tests. Replace the dependency and update those references to libxmljs; done means no libxmljs2 references remain and the test suite passes.

Written by the indexing model from the issue text.