Allow spread in Object Initializers with collection read-only property initialization

[datvm]

Right now, using inline spread for Object Initializers with collection read-only property initialization is not allowed:

int[] a = [1, 2, 3];

var f1 = new Foo()
{
    Items = { 1, 2, 3 }, // Valid
};

var f2 = new Foo()
{
    Items = { ..a }, // Error
};

public class Foo
{

    public List<int> Items { get; } = new();

}

Any reason this is not allowed? I am not sure what C# is attempting now but the error seems strange:

Cannot implicitly convert type 'int[]' to 'System.Index'

[datvm]

Sorry, duplicate of #8336