Add generics support in the type system

[TwitchBronBron]

Other languages (like TypeScript) have generics support. The BrighterScript type system should support them as well. For example:

function GetFirstItem<ListType>(list as List<ListType>)
    firstItem = list.First() as ListType
    return firstItem
end function

[markwpearce]

❤️

[markwpearce]

I assume class syntax would be similar?

class Queue<T>

  private data as T[] = []

  sub push(item as T)
    m.data.push(item)
  end sub

  function pop() as T
    return m.data.shift()
  end function

end class

[TwitchBronBron]

Yep I think that makes sense.