Add Get-EditorCommand and $psEditor.GetEditorCommand()

The way it is currently setup, it can be very difficult to determine what the Editor Command Names are that are loaded. The user is only shown the Display Name, so they will actually have to go look at the source code of the Register-EditorCommand to get the name.

This makes it difficult to unregister Editor Commands if you do not already know exactly what the command's name is. This will become more problematic once people start integrating their commands into modules.

首先跟踪现有的 Register-EditorCommand 流程，以及当前如何显示已加载的编辑器命令。当用户可以通过 Get-EditorCommand 和 $psEditor.GetEditorCommand() 发现编辑器命令名称，从而可以使用这些名称取消注册时，此更改即完成。