Add define_dataset_variable_order with OrderNumber sorting support (#791)

[RakeshBobba03]

#791 Implements define_dataset_variable_order metadata variable that returns dataset variables ordered by OrderNumber when present in Define XML, otherwise falls back to XML document order. This adds the new field to extract_dataset_metadata() and extract_domain_metadata() methods in BaseDefineXMLReader, updates all relevant dataset builders to include the field in their output, adds schema validation in MetaVariables.json, and includes comprehensive unit tests. The sorting logic is centralized in _get_ordered_dataset_variables() method following DRY principles.

[RamilCDISC]

The PR adds define_dataset_variable_order to dataset contents check against define xml. The updates were validated by:

1. Reviewing the PR for any unwanted code or comments.
2. Reviewing the PR logic in accordance with AC.
3. Ensuring all unit and regression testing pass.
4. Ensuring all relevant testing is updated.
5. Ensuring new tests are added for define_dataset_variable_order.
6. Running manual testing using CLI on positive datasets.
7. Running manual testing using CLI on negative datasets.
8. Running manual validation using dev editor on positive datasets.
9. Running manual validation using dev on negative datasets.
10. Covered cases like:

• when ordernumber is present
• when ordernumber is missing
• when only one ordernumber is missing
• when only one ordernumber is present
• when multiple ordernumbers are same
• when ordernumbers are in order in a row
• when a smaller ordernumber comes after a bigger ordernumber.