Provide emacs-29 behavior for register-preview

Provide emacs-29 behavior for register-preview

It is now the default with a value of register-use-preview eq to
basic.
To change this one have now to customize register-use-preview to
another value.

* lisp/register.el (register-preview-delay): Remove obsolescence.
(register--read-with-preview-function): New.
(register-use-preview): New option basic, it is now the default.
(register-preview-default-1): New the register-preview-default used by
`register-read-with-preview-fancy`.
(register-preview-default): Restored (same as Emacs-29).
(register--preview-function): Generic fn that return the right
function for register--preview-function.
(register-preview): Restored (same behavior as Emacs-29).
(register-preview-1): Used by `register-read-with-preview-fancy'.
(register-read-with-preview-basic): The old
register-read-with-preview.
(register-read-with-preview-fancy): The new
register-read-with-preview.