Disallow RequiresLocationAttribute in more places in source?

[jjonescz]

Currently, it is an error if user applies RequiresLocationAttribute to a parameter, but it's not an error if user applies it at other places. This is consistent with for example ParamArrayAttribute, but not with for example IsByRefLikeAttribute.

@AlekseyTs says in #68871 (comment):

let's confirm with LDM whether we want proactively prohibit application of the attribute in other contexts in order to preserve future design space.

Example:

SharpLab

using System;
using System.Runtime.CompilerServices;

[RequiresLocation] // currently no error, has no effect here
[ParamArray] // no error, has no effect here
[IsByRefLike] // error, use `ref struct` instead
public struct C
{
    public void M(
        [RequiresLocation] // error, use `ref readonly` instead
        [ParamArray] // error, use `params` instead
        [IsByRefLike] // error, although it has no effect here
        int p)
    {
    }
}

namespace System
{
    class ParamArrayAttribute : Attribute { }
}
namespace System.Runtime.CompilerServices
{
    class RequiresLocationAttribute : Attribute { }
    class IsByRefLikeAttribute : Attribute { }
}

[jaredpar]

My instinct here is that we should be disallowing in these cases. If we can squeeze this into 17.8 I would prefer that but I don't mind taking this as a small break in 17.9.