Compiler crash when attempting to define extension inside interface type

[DaZombieKiller]

Version Used:
4.14.0-3.25179.1 (304768b)

Steps to Reproduce:

Attempt to compile the following code:

interface IInterface
{
    extension(object)
    {
    }
}

Expected Behavior:
CS9283: Extensions must be declared in a top-level, non-generic, static class

Actual Behavior:
Process terminated. System.InvalidOperationException: Unexpected value 'Extension' of type 'Microsoft.CodeAnalysis.TypeKind'