Support modifier key to send mouse events to/through xterm.js, not terminal app

It'd be nice to be able to send mouse events to the process, not the terminal. Selecting tmux panes, scrolling in less, etc... These work in the Windows consoles, so there should be a way to make them work for us too.

I'll note that this doesn't even work in the VSCode terminal, which is my benchmark for xterm.js based terminals on Windows, so... This will likely have to wait until 1809 drops.

Based on some poking around for other reasons, this would likely involve some modifications around here: https://github.com/felixse/FluentTerminal/blob/14d111c4de295c8c0468525378535cdbd5bd40c2/FluentTerminal.RuntimeComponent/Interfaces/ITerminalEventListener.cs#L13