v2.29.0 - `int` and `double` share the same `num` interface

int and double now expose the same num interface

Each primitive only carried the conversion that changed its type: int had
toDouble() and double had toInt(), so the identity half of the pair was
missing on both. 3.toInt() and 1.5.toDouble() — both valid Dart, since
num.toInt() / num.toDouble() return this — failed with
Bad state: Can't find core function: int.toInt(...).

The same gap covered the rest of the num interface on int, which had none
of the members that only double had been given:

on int	before	now
toInt()	✗	✓ (identity)
round(), floor(), ceil(), truncate()	✗	✓ (identities)
toStringAsFixed(), toStringAsExponential(), toStringAsPrecision()	✗	✓
toDouble()	✓	✓

and on double, toDouble() is added as the matching identity.

This mattered most for a num-typed variable. ApolloVM has no num core
class, so num n = ... dispatches on the runtime value's class — meaning
n.toInt() worked or failed depending on whether n happened to hold a
double or an int. Both now work either way:

num n = 3;      // was: Can't find core function: int.toInt
n.toInt();      // 3
n.toDouble();   // 3.0

toNum() remains unsupported, as it is not a method on num, int or
double in Dart.