adds initial implementation to support ISL 2.0

[desaikd]

Description of changes:

This PR works on adding version configuration changes to allow ISL 2.0 support.

List of changes:

• fixes an issue with range construction which had a missing type check for range construction (95e97c973dfa06083227bfabda4813cceddaaefe)
• adds schema versioning configuration for all internal methods that were used to load schema or ISL model using an enum IonSchemaLanguageVersion(529fa2d02425d65bbda3062cda87ae0b5756c89e)
• isl_type, isl_type_reference and isl_constraint contains two modules with specific implementation of types/type references and constraints based on ISL version(v_1_0 and v_2_0). This will help with easier API modifications with new major/minor version release.
• All the previously defined schema model structs/enums are now hidden inside wrapper classes which helps with hiding implementation details based on ISL versioning.
  • e.g. IslType which was previously used to model an ISL type definition is now renamed as IslTypeKind. IslTypeKind has all the implementation details required to support both/all ISL version with a single struct. A new wrapper class that takes in this IslTypeKind to hide its implementation details. Along with that now IslTypeKind will be private to crate and users can only construct for IslType and use its accessor methods. In conclusion, all the wrapper classes are added to separate out implementation details from public facing APIs/structs.
  • Similar to IslType following structures are changed to add on a layer of abstraction from implementation layer.
  • IslConstraint enum has now changed to be called IslConstraintImpl. A wrapper class IslCosntraint is added on top of it that takes IslConstraintImpl to create the abstraction layer.
  • Similarly IslTypeRef is now called IslTypeRefImpl. And it has wrapper class that is called IslTypeRef.
• added UserReservedFields struct that stores user reserved fields for ISL 2.0.
• added validation for user reserved fields for ISL 2.0.
• adds methods to schema_system that converts ISL model to a resolved schema called schema_from_isl_schema.
  • schema_from_isl_schema makes sure that the given ISL model types contains the same version of ISL for their cosntraints. This check is not done while constructing the ISL model.
  • v_1_0 and v_2_0 modules does give user an idea on which ISL version they are using to construct the model but it does not guarantee that the model that is created has all the constraints from same version of ISL.
• IslSchema now has two methods to construct schema for a particular version schema_v_1_0 and schema_v_2_0.

Example construction of ISL model programmatically using the new signature:

Using a single ISL type to construct ISL schema model as below:

// an ISL 1.0 type that contains ISL 1.0 related constraints
let isl_type = isl_type::v_1_0::named_type(
    "my_type",
    [isl_constraint::v_1_0::element(
        isl_type_reference::v_1_0::named_type_ref("int"),
    )],
);
let isl = IslSchema::schema_v_1_0("sample.isl", vec![], vec![isl_type], vec![], vec![]);

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[desaikd]

Updates with latest changes:

• Makes simpler check for the ISL constraint version
• load_isl_schema doesn't need an argument for ISL version, instead checking the version marker
• Added mixed ISL constraints from different version tests
• ISL constraints v_1_0 and v_2_0 has its own implementation now to pass the proper ISL version.
• change in the Display for IonSchemaLanguageVersion enum