Improve foam.core.Function's Java support.
Improve foam.core.Function's Java support.

We can't serialize functions between java/js, but we can still use the
property type to store java's equivalent of a function using
java.util.function.Function

foam-framework/foam2,foam-framework/foam2,foam-framework/foam2,foam-framework/foam2,jacksonic/vjlofvhjfgm,jacksonic/vjlofvhjfgm,foam-framework/foam2,jacksonic/vjlofvhjfgm