kmacro: Simplify register code and recent change

kmacro: Simplify register code and recent change

While reviewing uses of `last-kbd-macro` for more problems like
those of bug#61700 I noticed that we don't need the `kmacro-register`
type any more (we can directly use the new `kmacro` type instead).
Also `macros.el` requires `kmacro` so rather than autoload
`macro--string-to-vector` it's simpler to move the function to
`kmacro.el`.  And while at it fold into it the `stringp` test that's used
before every call to that function.

* lisp/kmacro.el (kmacro--to-vector): Rename from
`macro--string-to-vector`, move from `mcros.el`, and make it work for
vectors.
(kmacro-ring-head, kmacro-lambda-form): Simplify accordingly.
(cl-print-object): Remove unused declaration.
(kmacro-register): Delete type.  Use `kmacro` objects instead.
(register-val-jump-to, register-val-describe, register-val-insert):
Rewrite accordingly.
(kmacro-to-register): Put the `kmacro` object.

* lisp/macros.el (macro--string-to-vector): Move to `kmacro.el`.
(insert-kbd-macro): Use `kmacro--to-vector`.

* src/macros.c (end_kbd_macro): Always generate a vector.