Fix edge case in InconsistentCapitalization

[PBoddington]

Currently, InconsistentCapitalization does not handle well the case that the class has multiple fields with names that are equivalent except for capitalization.

For example, the following code

class Test {
    
    private int abc;
    private int ABC;
    
    void foo(int ABC) {
    
    }
}

results in an error

[InconsistentCapitalization] Found the field 'abc' with the same name as the parameter 'ABC' but with different capitalization.

On the other hand, if the order of the fields is swapped, there is no match.

This proposed change improves the behaviour for this edge case, so that the order in which the fields are declared no longer matters. The new behaviour is that a parameter is a match if there is at least one field that is equivalent except for capitalization, but no field matches exactly.

[PBoddington]

I chose to use a List because using matchedFields.getFirst() is the simplest way to choose a matching field in a manner that is obviously deterministic. It would have to be a very weird class for the performance of iterating over the list to be a concern. However, I'd happily change the ListMultimap to something like a Map<String, Map<String, Symbol>> if requested.