MsgPack018 Unique names required in force map mode

[MessagePackObject]-attributed types may omit attributing each member with a [Key] attribute using forced map mode. In that mode, all serialized members must have unique names or a key collision would result in the serialized object.

Examples of patterns that are flagged by this analyzer

[MessagePackObject]
public class A
{
    public string Prop1 { get; set; }
}

[MessagePackObject]
public class B : A
{
    public new string Prop1 { get; set; } // Diagnostic reported here due to redefinition of Prop1
}

Typical fix

Rename one of the colliding properties:

[MessagePackObject]
public class A
{
    public string Prop1 { get; set; }
}

[MessagePackObject]
public class B : A
{
    public string Prop2 { get; set; }
}

Or add a [Key] attribute that assigns a unique serialized key to that member:

[MessagePackObject]
public class A
{
    public string Prop1 { get; set; }
}

[MessagePackObject]
public class B : A
{
    [Key("B_Prop1")]
    public new string Prop1 { get; set; }
}