gh-93202: Always use %zd printf formatter (#93201)

Python now always use the ``%zu`` and ``%zd`` printf formats to
format a size_t or Py_ssize_t number. Building Python 3.12 requires a
C11 compiler, so these printf formats are now always supported.

* PyObject_Print() and _PyObject_Dump() now use the printf %zd format
  to display an object reference count.
* Update PY_FORMAT_SIZE_T comment.
* Remove outdated notes about the %zd format in PyBytes_FromFormat()
  and PyUnicode_FromFormat() documentations.
* configure no longer checks for the %zd format and no longer defines
  PY_FORMAT_SIZE_T macro in pyconfig.h.
* pymacconfig.h no longer undefines PY_FORMAT_SIZE_T: macOS 10.4 is
  no longer supported. Python 3.12 now requires macOS 10.6 (Snow
  Leopard) or newer.