Ship bundled conpty on Windows

[lydell]

node-pty has started shipping conpty, instead of relying on the one shipped with Windows (which can be years behind). microsoft#694

The shipped binary is ~50 MB large, so we should only ship it on Windows.

[lydell]

As of 2024-08-06, the node-pty developers are actively working on this feature and pushing new beta versions regularly. We should wait until things have settled down.