adds changes to allow validating built-in types for TypeRef validation

[desaikd]

Description of changes: This PR works on adding changes for allowing validation for built-in types.

Example of the issue:

let schema = load_schema_from_text(r#" // No schema defined, uses built-in types"#);
// The following was only checking for types defined within schema but not built-in types
let type_to_validate = schema.get_type("int"); 
type_to_validate.validate(load_value("5"));

List of changes:

• adds implementation for validation of BuilInTypeDefinition
• removes redundant TypeDefinition checks for validation
• adds method in TypeStore to retrieve either a built-int type id or a defined type id based on the given type name

Test:

• adds test for built-in type validation