[kernel] Infinite loop when testing if two record types are equivalent

[nshahan]

DDC relies on the kernel implementation of DartTypeEquivalence to determine if some casts can be elided or replaced as null checks.

Some instances of record types can cause an infinite loop when checking if they are equivalent.

Originally reported here: flutter/flutter#129482

This code will cause the DDC compiler to hang:

main() {
  Object value = 'x';
  (a: 'a', b: value) as ({String a, String b});
}