Object parameters are considered to correspond depending on the order of declarations

Consider the following example (https://godbolt.org/z/6GvM438PM):
```cpp
struct D {
void f1(this D) {}
void f1(this D&) {} // rejected

void f2(this D&) {}
void f2(this D) {} // accepted

void g1(this D) {}
void g1() & {} // rejected

void g2() & {}
void g2(this D) {} // accepted
};
```
Similar to #187686, the order of declarations matters, even though it's not supposed to.
Note that well-formedness of all 4 examples is under consideration by P4138 that discusses CWG3103.
CC @cor3ntin

Reproduce the declaration-order differences in the linked Godbolt example, then compare the behavior with #187686 and the proposed treatment in P4138 and CWG3103. Trace the compiler's handling of object parameters and ref-qualified members; done means equivalent declarations receive consistent results regardless of declaration order, subject to the standard resolution.

Written by the indexing model from the issue text.