Python-style `Random` extensions for collections

[brcrista]

Python's random module has some convenient functions for working with sequences:

• https://docs.python.org/3/library/random.html#functions-for-sequences

C#'s Random class is pretty sparse by comparison: https://docs.microsoft.com/en-us/dotnet/api/system.random?view=netcore-3.1#methods

Make the following extension methods for Random:

• Choice()
• Choices()
• Shuffle()