Announce which buffer types are available on thumbnails elements

We recently changed it so kwin defaults to memptr because some clients
couldn't deal with dmabuf. We still want dmabuf to be used as it's less
stressful to the system and we support it just fine.

libtaskmanager/declarative/pipewiresourcestream.cpp

@@ -93,7 +93,9 @@ void PipeWireSourceStream::onStreamParamChanged(void *data, uint32_t id, const s
                                                                  SPA_PARAM_BUFFERS_stride,
                                                                  SPA_POD_CHOICE_RANGE_Int(stride, stride, INT32_MAX),
                                                                  SPA_PARAM_BUFFERS_align,
-                                                                 SPA_POD_Int(16));
+                                                                 SPA_POD_Int(16),
+                                                                 SPA_PARAM_BUFFERS_dataType,
+                                                                 SPA_POD_Int((1 << SPA_DATA_MemPtr) | (1 << SPA_DATA_MemFd) | (1 << SPA_DATA_DmaBuf)));
     pw_stream_update_params(pw->pwStream, &param, 1);
 }