Implement EQL query parser for EclipseLink.

[gregturn]

The following links are useful for capturing EclipseLink's support of both JPQL as well EQL:

• https://eclipse.dev/eclipselink/documentation/3.0/jpa/extensions/jpql.htm
• https://wiki.eclipse.org/EclipseLink/UserGuide/JPA/Basic_JPA_Development/Querying/JPQL

[gregturn]

There is also a flaw in the ref docs for EQL showing an invalid query. I opened eclipse-ee4j/eclipselink#1949 to alert the EclipseLink community.