Move cursor to its current location when editing a message with C-x

[osa1]

This was requested in the IRC channel once but I thought it's not possible.. until I realized that zsh's edit-command-line already does it when the editor is vim or emacs!

I think we should just implement the same idea. To summarize, if I have this line in the input line (where [] is the cursor):

blah blah blah []blah blah

and run e.g. vim by pressing C-x, I get the message copied in vim buffer, but the cursor will be at the beginning of the file.

As shown by the linked code, it's possible to move the cursor the its current location in vim and emacs. We should use the same idea and pass the cursor location to vim and emacs.