Modifies violation messages to include ISL struct for annoymous type definitions

[desaikd]

Issue #102:

Description of changes:

This PR works on adding ISL struct in the violation messages for anonymous type definitions. This adds more context in the violation message regarding where in the type definition the violation occurred.

List of changes:

• adds Display for TypeDefinition
• adds isl_type_struct field in IslTypeImpl and TypeDefinitionImpl that represents ISL type struct in string format
• remove usage of Debug for violation messages and instead uses Display. (Change all the {:?} usage to {})
• modifies tests accordingly

Example of a violation message: Schema:

type::{
  name: one_of_type,
  one_of: [ { type: string, codepoint_length: range::[1, 10] }, decimal ],
}

Type to be validated:

one_of_type

Ion value used for validation:

1

New violation message changed with this PR:

Violation {
    constraint: "one_of_type",
    code: TypeConstraintsUnsatisfied,
    message: "value didn't satisfy type constraint(s)",
    violations: [
        Violation {
            constraint: "one_of",
            code: NoTypesMatched,
            message: "value matches none of the types",
            violations: [
                Violation {
                    constraint: "{type: string, codepoint_length: range::[1, 10]}",  // <--- gives a more precise location information
                    code: TypeConstraintsUnsatisfied,
                    message: "value didn't satisfy type constraint(s)",
                    violations: [
                        Violation {
                            constraint: "type_constraint",
                            code: TypeMismatched,
                            message: "expected type String, found Integer",
                            violations: [],
                        },
                        Violation {
                            constraint: "codepoint_length",
                            code: TypeMismatched,
                            message: "expected [String, Symbol] but found integer",
                            violations: [],
                        },
                    ],
                },
                Violation {
                    constraint: "type_constraint",
                    code: TypeMismatched,
                    message: "expected type Decimal, found Integer",
                    violations: [],
                },
            ],
        },
    ],
}

Previous violation message (prior tot his PR):

Violation {
    constraint: "one_of_type",
    code: TypeConstraintsUnsatisfied,
    message: "value didn't satisfy type constraint(s)",
    violations: [
        Violation {
            constraint: "one_of",
            code: NoTypesMatched,
            message: "value matches none of the types",
            violations: [
                Violation {
                    constraint: "",
                    code: TypeConstraintsUnsatisfied,
                    message: "value didn't satisfy type constraint(s)",
                    violations: [
                        Violation {
                            constraint: "type_constraint",
                            code: TypeMismatched,
                            message: "expected type String, found Integer",
                            violations: [],
                        },
                        Violation {
                            constraint: "codepoint_length",
                            code: TypeMismatched,
                            message: "expected [String, Symbol] but found integer",
                            violations: [],
                        },
                    ],
                },
                Violation {
                    constraint: "type_constraint",
                    code: TypeMismatched,
                    message: "expected type Decimal, found Integer",
                    violations: [],
                },
            ],
        },
    ],
}

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