C# 7.2 added support for the new access modifier private protected.

This is used for the following public methods:

• HaveAccessModifier
• NotHaveAccessModifier
• WhichSetterHas
• WhichSetterDoesNotHave
• WhichGetterHas
• WhichGetterDoesNotHave
• BeWritable
• BeReadable

It would be nice to have support for private protected.

This should be accomplishable by:

• Adding another enum to CSharpAccessModifier.cs,
• add a check for IsFamilyAndAssembly for the methods in
  CSharpAccessModifierExtensions.cs, and
• write some tests