seq-every-p documentation suggestion

[R. Clayton]

The documentation for seq-every-p is incomplete because it specifies a function
satisfied by the definition

  (defun seq-every-p (P S) t)

which I'm assuming isn't an acceptable implementation for seq-every-p.  One
potential fix is to rewrite the specification as

  Return non-nil if and only if PRED returns non-nil for all the elements of
  SEQUENCE.

or more explicitly

  Return non-nil if PRED returns non-nil for all the elements of SEQUENCE,
  otherwise return nil. 

The documentation should also describe what is expected when S is the empty
list.

This is in emacs 29.1 on Debian testing.