Implementation of equals() API for dom.Value

[desaikd]

Issue #663

Description of changes:
This PR implements the equals API for dom.Value.

Terminology:

• Strict equivalence:
  It refers to Ion data model equivalence as defined above and by Ion Specification

• Structural or non strict equivalence:
  It follows the same rules as strict equivalence, except that

  • Annotations are not considered, and
  • Timestamps that represent the same instant in time are always considered equivalent.

equals():
This method can be used on each dom.Value for checking it's equivalence with other dom.Value. It return a boolean value representing whether both values are equal or not.

Options:
This method has additional options for equivalence as below:
epsilon is used by Float for an equality with given epsilon precision. (Default: null)
strict specifies whether equality should be strict or non strict. (Default: true)

Tasks:

1. Created an equals() method in dom.Value for implementation.
2. Created an ionEquals() method that cam be used as a helper method inside equals() for each dom.Value specific equivalence logic.
3. Implemented ionEquals() for each dom.Value type.

Test:
Created equivalence unit tests for each dom.Value Ion data types.

[zslayton]

👍