Undocumented attribute: Forcetokenstabilizationattribute & __Dynamicallyinvokableattribute

Question

I discovered an attribute undocumented, and he is Friend, is located in the namespace System.Runtime.CompilerServices, as it is used in the system, it has no documentation. I tried to decompile this attribute and received this source:

<AttributeUsage(AttributeTargets.[Class] Or AttributeTargets.Struct Or AttributeTargets.[Enum] Or AttributeTargets.Constructor Or AttributeTargets.Method Or AttributeTargets.[Property] Or AttributeTargets.Field Or AttributeTargets.[Event] Or AttributeTargets.[Interface]), FriendAccessAllowed()>
Friend Class FriendAccessAllowedAttribute
   Inherits Attribute

   <TargetedPatchingOptOut("Performance critical to inline this type of method across NGen image boundaries")>
   Public Sub New()
   End Sub
End Class

also came this class, called __DynamicallyInvokableAttribute:`

<AttributeUsage(AttributeTargets.All)>
Public Class __DynamicallyInvokableAttribute
   Inherits Attribute

   <TargetedPatchingOptOut("Performance critical to inline this type of method across NGen image boundaries")>
   Public Sub New()
   End Sub
End Class

both are not documented, but what they are and what they serve?