Only show applicable registers in *Register preview* buffer

Only show applicable registers in *Register preview* buffer

* lisp/register.el (register-preview-default): Doc fix.
(register-read-with-preview): Preserve 'last-input-event' when calling
'y-or-n-p'.  New optional argument PRED, pass it to...
(register-preview): New optional argument PRED.
(register-jump-p, register-insert-p, register-increment-p): New func.
(jump-to-register, increment-register, insert-register)
(append-to-register, prepend-to-register): Update.
* doc/lispref/text.texi (Registers): Update
'register-read-with-preview' documentation.
* etc/NEWS: Announce it.