GetTypeInfo returns incorrectly null-annotated types for deconstruction

[DoctorKrolic]

Version Used:
4.7.0-1.final

Steps to Reproduce:

using Microsoft.CodeAnalysis;
using Microsoft.CodeAnalysis.CSharp;
using Microsoft.CodeAnalysis.CSharp.Syntax;

var code = """
    #nullable enable

    class C
    {
        public void Deconstruct(out string? s1, out string? s2)
        {
            s1 = null;
            s2 = null;
        }

        void M(C[] items)
        {
            var item = items[0];
            var (s1, s2) = item;

            foreach (var (s3, s4) in items)
            {

            }
        }
    }
    """;

var syntaxTree = CSharpSyntaxTree.ParseText(code);

var compilation = CSharpCompilation.Create("Test", new[] { syntaxTree }, new[] { MetadataReference.CreateFromFile(typeof(object).Assembly.Location) });
var semanticModel = compilation.GetSemanticModel(syntaxTree);

var root = syntaxTree.GetRoot();

var assignmentExpression = root.DescendantNodes().OfType<AssignmentExpressionSyntax>().ElementAt(2);
var typeSyntax = ((DeclarationExpressionSyntax)assignmentExpression.Left).Type;
var typeInfo = semanticModel.GetTypeInfo(typeSyntax);

Console.WriteLine(typeInfo.Type);

var foreachStatement = root.DescendantNodes().OfType<ForEachVariableStatementSyntax>().Single();
typeSyntax = ((DeclarationExpressionSyntax)foreachStatement.Variable).Type;
typeInfo = semanticModel.GetTypeInfo(typeSyntax);

Console.WriteLine(typeInfo.Type);

Expected Output:

(string? s1, string? s2)
(string? s3, string? s4)

Actual Output:

(string s1, string s2)
(string s3, string s4)

This is the root cause of #47038. Fixing it should automatically fix #47038 as well.

This is also observable in IDE. If you hover over any s variable, the quick info will show correct string? type, but if you hover over var, it will show tuple without nullability annotations: