fix enum reflection based partial_cmp, disallow compare different variant names.

[molikto]

Objective

Fix #22586

The problem is in #22452 I used variant_index to compare two enum values. Because I want to maintain:

• if you have a,b: A and tries call a.reflect_partial_cmp(b), the result should align with the version derived on A.

But appearently for dynamic types and also a: A; b: B different types, the behaviour is a bit chaotic. (see #22586)

Solution

Don't compare by variant_index anymore. It's a different tradeoff, but I think it's a more sensible one.

Testing

Modified unit tests