Migrate GREL to the Truffle framework

Is your feature request related to a problem or area of OpenRefine? Please describe.
It would be nice to re-implement GREL using the Truffle library, which is used by GraalVM to implement interpreters for various languages.
This would bring the following benefits:

• ability to improve interoperability between expression languages: for instance, using some GREL functions in other expression languages or conversely;
• potentially a faster evaluation if the GraalVM is used (although given GREL's simplicity I would not expect huge gains);
• allowing Truffle-based AST analysis, for #2248.

Describe the solution you'd like
Expose GREL as a Truffle-compatible language.

Additional context
This is not a blocking feature in our roadmap, it would just be a nice thing to have on the long term. It should also be a good first task to learn about Truffle.

Start by reviewing how GREL is currently implemented and how Truffle-based languages are exposed in GraalVM. Consider the AST analysis goal described in #2248 and the requested interoperability benefits. Done means GREL is exposed as a Truffle-compatible language without making it a roadmap-blocking requirement.