No error reported for overload ambiguity with extension methods with identical signatures and params arrays

[cston]

Version Used:

main: 7ecf61f

Steps to Reproduce:

Compile the following:

using System.Collections;
using System.Collections.Generic;

class MyCollection<T> : IEnumerable<T>
{
    IEnumerator<T> IEnumerable<T>.GetEnumerator() => throw null;
    IEnumerator IEnumerable.GetEnumerator() => throw null;
}

static class ExtensionsA
{
    public static void Add<T>(this MyCollection<T> collection, params string[] args) { }
}

static class ExtensionsB
{
    public static void Add<T>(this MyCollection<T> collection, params string[] args) { }
}

class Program
{
    static void Main()
    {
        var x = new MyCollection<object>();
        x.Add("");
        
        var y = new MyCollection<object> { "" };
    }
}

Expected Behavior:

The following errors are expected, as reported by 4.10.0-3.24161.9 (b0be498).

(25,11): error CS0121: The call is ambiguous between the following methods or properties:
    'ExtensionsA.Add<T>(MyCollection<T>, params string[])' and
    'ExtensionsB.Add<T>(MyCollection<T>, params string[])'
(27,44): error CS0121: The call is ambiguous between the following methods or properties:
    'ExtensionsA.Add<T>(MyCollection<T>, params string[])' and
    'ExtensionsB.Add<T>(MyCollection<T>, params string[])'

Actual Behavior:

No errors.

[cston]

cc @AlekseyTs

[AlekseyTs]

It looks like IsBetterCollectionExpressionConversion is not designed to be called with identical type, which happens for params scenario from IsBetterParamsCollectionType.