RationalNode numerator & denominator fields to make it directly usable

[eregon]

Rational literals are either:

• 123r
• 12.34r

(12ri/12.34ri is just ImaginaryNode of RationalNode, so a trivial variant)

These are actually quite different, the first is the same as Rational(123, 1) but the second is Rational(1234, 100), not Rational(12.34):

irb(main):001:0> 12.34r
=> (617/50)
irb(main):002:0> Rational(1234, 100)
=> (617/50)
irb(main):003:0> Rational(12.34)
=> (3473401212609495/281474976710656)

So right now to handle this we have to manually parse the number, e.g. TruffleRuby does it like this:
https://github.com/oracle/truffleruby/blob/5096dddf6c3adc7edbae0938efc4fb4913b62bba/src/main/java/org/truffleruby/parser/YARPTranslator.java#L2905-L2927

It would be great if RationalNode was changed to have a numerator and denominator field, then we wouldn't need to manually reparse the number.
It could also potentially save an unnecessary conversion from string to double, since the double value in this case should not be used anyway.

code	before	after
123r	RationalNode(numeric=IntegerNode(123))	RationalNode(numerator=IntegerNode(123), denominator=IntegerNode(1) (or nil))
12.34r	RationalNode(numeric=FloatNode(12.34))	RationalNode(numerator=IntegerNode(1234), denominator=IntegerNode(100))

cc @andrykonchin

[eregon]

@kddnewton Should this be addressed for 1.0, since it will likely be a breaking change for consumers?
Although maybe it's feasible to define a numeric method for compatibility.

[kddnewton]

Yeah this is already out! There's a numeric method for backwards compat as well.

[kddnewton]

Oh this can be closed now.

[eregon]

Sweet!
@andrykonchin Could you adopt this in TruffleRuby? It should simplify a bunch of logic.
It also looks (from the docs) that Prism does the canonicalization, so we could skip that when creating the Rational from the literal.

[kddnewton]

It only does the reduction if it fits into 32-bits unfortunately. I haven't implemented the bignum stuff yet.