Add support for `nxWriteFrame` to Input sessions

[epage]

nxWriteFrame is overloaded. For output modes, its behavior is obvious. For input modes:

Any signal or frame input mode: The Buffer parameter is ignored, and you can set it to NULL. The function transmits an event remote frame.

We need to add support for this to our input modes.

[epage]

I had a discussion with @lilesj about what to name this.

It

• writes/transmits/sends an event remote frame
• to request frames from the remote interface

So we discussed names that focused on one or the other of those. We landed on request_remote_frame (or frames?).