[XML-to-XSD] Support XSD validation for `data.xmldata`module

[SasinduDilshara]

There are few sub tasks in this task

• [x] https://github.com/ballerina-platform/ballerina-library/issues/6936
• [ ] https://github.com/ballerina-platform/ballerina-library/issues/6937

[SasinduDilshara]

Currently, the Flat sequences and Flat choice elements in the XSD are implemented with the tests according to the https://docs.google.com/document/d/1nz-Osw3kyLpSzkBfZkGIcM0BPzth_ScEVeatAYrXFMw/edit?tab=t.0#heading=h.xzw1i3ooqc6v

Had a offline chat with @MaryamZi and @hasithaa to discuss about the priority subtasks and implementations of nested sequences /choices in this feature and working according to that. I will update this issue with future implementation details

[SasinduDilshara]

Created a document with possible XML to record options https://docs.google.com/document/d/1rc6QGqgmrqph5cbd5kWlJEbc4A9zFBIwc-mfnkmTJ_I/edit?usp=sharing Currently this is under the review

[SasinduDilshara]

I was able to implement the XSD choice, choice arrays, XSD sequences and sequences arrays for the XSD along with Element occurences.

Following are some testcases with the implementation