Specially decode more selection types on Haiku

Specially decode more selection types on Haiku

* src/haiku_select.cc (be_get_point_data, be_add_point_data):
New functions.
* src/haikuselect.c (haiku_message_to_lisp, lisp_to_type_code)
(haiku_lisp_to_message): Accept new types `size_t', `ssize_t'
and `point'.
(Fhaiku_drag_message): Update doc string.
(syms_of_haikuselect): New defsyms.
* src/haikuselect.h: Update prototypes.