Introduce frame_info_ptr smart pointer class

This adds frame_info_ptr, a smart pointer class.  Every instance of
the class is kept on an intrusive list.  When reinit_frame_cache is
called, the list is traversed and all the pointers are invalidated.
This should help catch the typical GDB bug of keeping a frame_info
pointer alive where a frame ID was needed instead.

Co-Authored-By: Bruno Larsen <blarsen@redhat.com>
Approved-by: Tom Tomey <tom@tromey.com>