feat: Kill child processes when task shell receives ctrl-c

[mo]

When running docker compose from "deno task" you get bad CTRL-C handling compared to "npm run". This problem can be reproduced by running "npm run docker-compose" and "deno task docker-compose" in this minimal testcase repo:
https://github.com/mo/deno-tasks-signal-issue-repro

There is some more info in this issue:
#33

The main purpose of the PR is to make sure all of these behave well with ctrl-c:
{
  "tasks": {
    "docker-compose": "./docker-compose.sh",
    "docker-compose-no-sh-file": "docker compose -f compose.yaml up",
    "sleep": "sleep 999",
    "simple-builtin": "echo hello",
    "simple-bin": "date",
    "cmd": "cat /dev/urandom | head -c 1000000 | sha256sum",
    "hashpipe-slow": "$(which cat) /dev/urandom | $(which head) -c 1000000000 | sha256sum",
    "hashpipe-slower": "$(which cat) /dev/urandom | $(which head) -c 10000000000 | sha256sum",
    "forever-pipe": "yes | grep -v mystery | grep -v magic | sort | uniq -c",
  }
}

When this PR is applied, "deno task docker-compose" works similar to "npm run", however the code is the PR needs some cleanup.

I tried to clean it up by not spawning a tokio task however that version doesn't solve the main docker compose use case and unfortunately I don't understand why that is. This version also prints some debug info with a new empty lines just to make sure the debug print outs doesn't get overwritten by the docker compose "progress" printouts:
mo@7514eba

@dsherret already provided some feedback on needed cleanup of this PR in an earlier PR which was incorrectly pushed with the PR-commit directly on "main".. so the current PR just aims to re-create the PR so that maintainer edits are possible. The old PR was:
#125

[rf-molsson]

@dsherret if you have some other fix in mind, feel free to discard this PR and merge your own fix instead... I mostly want the issue fixed... and I'd be happy to test our your PR if you create an alternative one, just ping me

[dsherret]

Closing in favour of #131