emacs: Support auto-updating after performing REPL operation.

emacs: Support auto-updating after performing REPL operation.

* emacs/guix-backend.el (guix-operation-buffer): New variable.
  (guix-eval-in-repl): Use it.  Add optional 'operation-buffer' argument.
* emacs/guix-base.el (guix-update-after-operation): New variable.
  (guix-switch-to-buffer, guix-list-or-info-buffer-p, guix-buffers,
  guix-update-buffers-maybe): New procedures.
  (guix-set-buffer): Use 'guix-switch-to-buffer'.  Add optional 'no-display'
  argument.
  (guix-process-package-actions, guix-delete-generations,
  guix-switch-to-generation): Add optional 'operation-buffer' argument.
* emacs/guix-info.el (guix-package-info-insert-action-button,
  guix-generation-info-insert-number, guix-generation-info-insert-current):
  Adjust for using operation buffer.
* emacs/guix-list.el (guix-list-execute-package-actions,
  guix-generation-list-switch, guix-generation-list-execute): Likewise.