Avoid allocating Lisp_Save_Value for arrays

Avoid allocating Lisp_Save_Value for arrays

* src/alloc.c (mark_maybe_objects): New function.
* src/eval.c (default_toplevel_binding)
(backtrace_eval_unrewind, Fbacktrace__locals):
Treat array unwindings like other miscellaneous pdl types.
(record_unwind_protect_array): New function.
(do_one_unbind): Free the array while unwinding.
(mark_specpdl): Mark arrays directly.
* src/lisp.h (SPECPDL_UNWIND_ARRAY): New constant.
(union specbinding): New member unwind_array.
(SAFE_ALLOCA_LISP_EXTRA): Use record_unwind_protect_array
instead of make_save_memory + record_unwind_protect.