tsc --watch should listen for stdin requests to transpile on demand

[ORESoftware]

nodemon will listen for "rs" streaming to process.stdin and this allows the user to manually restart a process.

In the same way, there are times where it would be nice to manually restart an incremental build with tsc --watch, although it might not be much faster since it will rebuild everything, it should be a little smoother.

[DanielRosenwasser]

I think a more interactive --watch that ties this in with #13020 would be very nice.