Update to Groovy 3.x

[wimdeblauwe]

This will avoid the problem of the reflective access warning (issue #188)

[mjeffrey]

It'd be nice to have this before Java 17 where this warning changes to an error (java17 removes the possibility to ignore the error).

See https://blogs.oracle.com/javamagazine/java-runtime-encapsulation-internals

[ultraq]

Oh hey, thanks for letting me know that this was finally gonna be clamped down in Java 17. I've had a Groovy 3 branch that needed some cleaning up to work correctly, so I've completed that work which closes this issue and am aiming for it to be in the next major version.

If anybody coming across this issue is interested, there is a 3.0.0-SNAPSHOT version of the layout dialect that contains this upgrade.

[mjeffrey]

Thank you! Will try out the snapshot.