INT-3503 equals & hashCode for ToStringFriendlyJN

JIRA: https://jira.spring.io/browse/INT-3503

**Cherry-pick to 4.0.x**

PR Comments and test
INT-3509 Add Convert Node & DOMSource to Document

JIRA: https://jira.spring.io/browse/INT-3509

**Cherry-pick to 3.0.x and 4.0.x**

Polishing

- Javadoc
- Refactor duplicated code