Fixes #27343
Currently the node:child_process polyfill is always passing the full
parent environment to all spawned subprocesses. In the case where
`options.env` is provided those keys are overridden but the rest of the
parent environment is still passed through.
On Node the behaviour is for child processes to only inherit the parent
environment when `options.env` isn't specified. When `options.env` is
specified the child process inherits only those keys.
This PR updates the internal node child_process polyfill so that the
`clearEnv` argument is set to true when spawning the subprocess to
prevent the parent environment always being inherited by default. It
also fixes an issue where `normalizeSpawnArguments` wasn't returning the
`env` option if `options.env` was unset.
5a39f2f096