Add a new command in VSMac that lists all the other available commands

[nosami]

Feature category

• Check(Type 'x') any that Applicable item:
  • Vim
  • Vim plugin

re: #3006

It would be useful to be able to list all the available commands in VSMac that can be bound with keypresses via the vimrc file.
I think I would just use the built in logging mechanism to log to the Vim output pad in VSMac.

It could be invoked with something like :vsc VsVim.ListAllCommands