add AdvancedDebuggerDisplayExtensions

[InsanityCode]

Problem

The DebuggerDisplayAttribute does not recursively evaluate the DebuggerDisplayAttribute of types used in the provided debugger display expression.

Sadly the DebuggerDisplayAttribute class is sealed, so inheriting this class and defining a custom attribute for that sake is not an option.

Solution

Provide an extension method for all types that evaluates the debugger display of an object.

[InsanityCode]

As it is now this is far from complete as it is lacking support for several kinds of expressions supported by
DebuggerDisplayAttributes, such as

• passing arguments to called methods
• accessing static members
• indexers
• escaping braces by using double braces:
  e.g. {{ this is not an expression to be evaluated, but a terminal }}
• calling extension methods on an object
  (other than .DebugDisplay())
• arithmetic or logical operators
• expressions in parantheses

... and likely many more

The status quo is simply meant to present the concept in order to decide whether we actually want that.

[FramePerfection]

Unfortunately I could not get this to work at all in Visual Studio 2017, it would always fail to find the DebugDisplay extension method, no matter how I tried to qualify it.

On top of this, the amount of Todos is already considerable, and it's unlikely that many of the features required to fully support all sorts of C# expressions would find much use anyways.

I believe the solution here is to just take the hit and explicitly parameterize the DebuggerDisplay attribute as necessary where it really is necessary. It won't do to attempt changing the fundamental behavior of a piece of software that we have essentially no control over, and given that dotnet/roslyn#24670 is probably not going to be resolved any time soon, there's nothing we can really do.