Some time ago there was a property _FREERDP_CLIPRDR_ID which was indended
to indicate that an XFreeRDP window owns a clipboard. This was necessary
for raw transfers. This property was used by xf_cliprdr_is_self_owned()
function. However, raw transfer support was broken and the meaning of
xf_cliprdr_is_self_owned() gradually changed into checking whether
the *current* window owns the clipboard, not just any XFreeRDP window.
Thus _FREERDP_CLIPRDR_ID was removed in a4580923e77b4690 (xfreerdp/clipr:
fix self owned test and hardening).
However, now we are going to fix raw transfers and we need that property.
This patch reintroduces a similar property "_FREERDP_CLIPRDR_RAW" which
indicates that a window is an XFreeRDP window with enabled raw transfer.
It is currently used by xf_cliprdr_server_format_data_request() to
correctly request format data from another XFreeRDP instance via raw
transfer protocol.
This property can be queried from the clipboard owner with the function
xf_cliprdr_is_raw_transfer_available() and can be enabled or disabled
on the current window by xf_cliprdr_set_raw_transfer_enabled().
Disabling raw transfers will be necesary to correctly implement file
transfers in the future. However, currently raw transfers are always
enabled.