Implement selection ownership on Haiku

Implement selection ownership on Haiku

* lisp/term/haiku-win.el (haiku-selection-owner-p): New
declaration.
(gui-backend-selection-owner-p): Implement using newly exposed
primitive.

* src/haiku_select.cc
(count_clipboard, count_primary, count_secondary): New
variables for tracking selection ownership.
(BClipboard_set_system_data):
(BClipboard_set_primary_selection_data):
(BClipboard_set_secondary_selection_data): Set ownership
variables.
(BClipboard_owns_clipboard):
(BClipboard_owns_primary):
(BClipboard_owns_secondary): New functions.

* src/haikuselect.c (Fhaiku_selection_owner_p): New function.
(syms_of_haikuselect): Define new subr.
* src/haikuselect.h: New prototypes.