Store latin-1 content into the Haiku clipboard as well

Store latin-1 content into the Haiku clipboard as well

* lisp/term/haiku-win.el (haiku-normal-selection-encoders): New
variable.
(haiku-select-encode-utf-8-string, haiku-select-encode-xstring):
New functions.
(gui-backend-set-selection): Use new selection encoder functions
instead of hard-coding UTF-8.
(haiku-dnd-handle-drag-n-drop-event): Rename to
`haiku-drag-and-drop'.

* src/haiku_select.cc (be_lock_clipboard_message): Accept new
argument `clear'.
(be_unlock_clipboard): Accept new argument `discard'.

* src/haikuselect.c (Fhaiku_selection_data): Change calls to
`be_lock_clipboard_message' and `be_unlock_clipboard'.
(haiku_unwind_clipboard_lock): New function.
(Fhaiku_selection_put): Accept new meaning of `name' which means
to set the selection message.

* src/haikuselect.h: Update prototypes.