Fix NS frame parameters (bug#39000)

Fix NS frame parameters (bug#39000)

* src/frame.c (make_frame): Use new system default setting.
* src/frame.h (enum ns_appearance_type): Add new system default
setting.
* src/nsfns.m (Fx_create_frame): Correctly handle Qunbound and support
system default appearance.
(syms_of_nsfns): Add Qlight.
* src/nsterm.h: New method definition.
* src/nsterm.m (ns_set_appearance): Correctly handle Qlight and use new
setAppearance method.
([EmacsView initFrameFromEmacs:]): Use new setAppearance method.
([EmacsWindow setAppearance]): New method.
* doc/lispref/frames.texi (Management Parameters): Document 'light'.