bug#46621: Copy line

[Drew Adams]

> > I don't believe everyone would agree on such short keys.
> 
> Quite the contrary, they definitely would! What they wouldn't agree on
> is what pre-existing binding to repurpose.
> Fortunately there are still a few single-key bindings available.
> 
> > Maybe better to try finding a key in the 'C-x x' keymap
> > (that already contains a line-related binding 'C-x x t'
> > `toggle-truncate-lines').
> 
> Unfortunately that removes some of the convenience that the command
> would bring. I can't see anyone typing `C-x x d` (for example) 3 times
> in a row to get 3 copies, much less 7 times.

FWIW, I don't agree that _any_ keys should be bound
by default for such a command.

Do not add a new command and immediately give it a
default key binding.  That makes little sense.

Let user experience guide spending/wasting default
keys.  Users can bind the command to any key they
like.  If it becomes super popular, and if there are
good reasons at that point to give it a default key,
then you can take into account the keys that users
at that point say they like for it.

Emacs has survived well for 40 years without such a
command.  Just because someone asks for it now is
not a reason that it deserves a default key binding.

There are tons of keys that deserve bindings before
this one does.

Binding this new command to a default key is just
irrational exuberance.