CallerMemberNameAttribute on non-function member

**Describe the bug**

The standard does not specify what becomes the default value of a parameter decorated with CallerMemberNameAttribute when the parameter belongs to a constructor of an attribute, and a property or an indexer (or a type parameter of an indexer) is decorated with this attribute. (The standard specifies this if an *accessor* of a property or indexer is so decorated.)

C# 9 draft section 23.5.6.4 The CallerMemberName attribute.

**Example**

```csharp

using System;
using System.Runtime.CompilerServices;

public class MAttribute : Attribute {
public MAttribute(
[CallerMemberName]string? name = null) {
}
}

class C {
[M] object o = new MAttribute();

[M] object P {
[M] get => new MAttribute();
}

[M] object this[[M]int index] {
[M] get => new MAttribute();
}

[M] delegate void D<[M]T>();
}
```

**Expected behavior**

Should be equivalent to:

```csharp
class C {
[M(null)] object o = new MAttribute("o");

[M("P")] object P {
[M("P")] get => new MAttribute("P");
}

[M("Item")] object this[[M("Item")]int index] {
[M("Item")] get => new MAttribute("Item");
}

[M(null)] delegate void D<[M(null)]T>();
}
```

**Additional context**

Noticed from .