Tuple implementation rejects implicit operators

[gafter]

The following code is improperly rejected by the tuple implementation

namespace System
{
    public struct ValueTuple<T1, T2>
    {
        public T1 Item1;
        public T2 Item2;

        // error: conversion must convert to or from enclosing type
        public static implicit operator Collections.Generic.KeyValuePair<T1, T2>(ValueTuple<T1, T2> tuple)
        {
            T1 k;
            T2 v;
            (k, v) = tuple;
            return new KeyValuePair<T1, T2>(k, v);
        }

        // error: conversion must convert to or from enclosing type
        public static implicit operator ValueTuple<T1, T2>(Collections.Generic.KeyValuePair<T1, T2> kvp)
        {
            return (kvp.Key, kvp.Value);
        }
    }
}

This was tested against https://github.com/jcouv/roslyn/tree/tuple-deconstruction (from #11457) at commit jcouv@c7b60a4

[AlekseyTs]

@gafter Could you confirm that you have #11328 merged when you see the errors?

[jcouv]

You may want to try those tests in the future branch, which has the latest tuple code.
Only deconstruction-specific tests make sense in the features/tuples branch at this point.

[gafter]

@AlekseyTs I am no longer working on the branch from which I reported this. I've identified the specific branch that I was testing. You are welcome to verify whether or not that branch contains #11328.