This commit adds `--eval` flag to `deno task` subcommand.
This flag allows to evaluate provided "task name" as a task itself,
effectively allowing to use `deno_task_shell` from the command line.
Also fixes shebang parsing for `node_modules/.bin/` entries to handle
`#!/usr/bin/node -S node` in addition to `#!/usr/bin/node node`.
Closes https://github.com/denoland/deno/issues/26918
