New variable 'expose-hidden-buffer' (Bug#75828)

New variable 'expose-hidden-buffer' (Bug#75828)

* src/frame.c (make_frame): Handle 'expose-hidden-buffer'.
(expose-hidden-buffer): New variable to handle hidden buffers.
* src/buffer.c (Fother_buffer): Mention that it does not return
a hidden buffer.
* lisp/frame.el (make-frame): In doc-string describe handling
of hidden buffers.
* doc/lispref/frames.texi (Creating Frames): Explain handling
of hidden buffers in description of 'make-frame'.

(cherry picked from commit 7f01dd8906cbc8839ffecc55cfa7ff789f3fa298)