FCPPluginClient.send(): Add draft of function for splitting it up even
more

- The long name is to be symmetric to the other function with the long
name maybeDispatchMessageLocallyToSendSynchronousThread, see
3b882af127bbf8543f63d9af716e291769fb063c for the justification
of that one. The most important reasons apply here as well, for example
the fact that the function is only used once internally.
FCPPluginClient.send(): Prepare the final splitup

- This only moves the unmodified code, it is not adapted to be sane in
the context of the backend function yet. The following commits will
adapt it.