Comparison functions should use new features from Set

[paceaux]

Set now has new data comparison features:

• .difference()
• .intersection()
• symmetricDifference()
• .union()
• .disjointFrom()

The functions.comparisons.ts should be refactored to use these rather than the built in versions.

All existing tests should continue to pass.

[paceaux]

Apparently there's some sort of problem between either Babel, Jest, or ts-jest where the unit tests fail saying set.union is not a function. Like a lying bastard.

[paceaux]

Turns out this requires the use of shims because pre-Node-20 these methods aren't available on the prototype.

so the functions have been refactored slightly to use the shims, which obviously will be less necessary in a year or two.