Restore cua-delete-copy-to-register-0 and M-v command.

Restore cua-delete-copy-to-register-0 and M-v command.
* lisp/delsel.el (delete-selection-save-to-register)
(delsel--replace-text-or-position): New vars.
(delete-active-region): Use them.
(delete-selection-repeat-replace-region): New command, moved from
cua-base.el.
* lisp/emulation/cua-base.el (cua--repeat-replace-text): Remove var.
(cua-repeat-replace-region): Move command to delsel.el.
(cua--init-keymaps): Update binding accordingly.
(cua-mode): Set delete-selection-save-to-register.

Fixes: debbugs:18886