feat: terminate spawned processes when the deno task process is terminated on Windows

[dsherret]

I have a test for this in the CLI here: https://github.com/denoland/deno/pull/14421 -- I wasn't sure how to test this here.

This uses the jobs api in Windows in order to accomplish this.

Closes #33

[piscisaureus]

I wasn't sure how to test this here.

If you need ideas...

• spawn a process that never exits (e.g. cmd.exe /c pause)
• add the process handle to the job object
• drop the job objec - this should kill the process
• wait for the process handle. Without the job object this should hang. With it, it should return.