This change lets us set runtime specific options in Pulumi.yaml, which
will flow as arguments to the language hosts. We then teach the nodejs
host that when the `typescript` is set to `true` that it should load
ts-node before calling into user code. This allows using typescript
natively without an explicit compile step outside of Pulumi.
This works even when a tsconfig.json file is not present in the
application and should provide a nicer inner loop for folks writing
typescript (I'm pretty sure everyone has run into the "but I fixed
that bug! Why isn't it getting picked up? Oh, I forgot to run tsc"
problem.
Fixes#958
ce5eaa8343