ensure webpack worker exits bubble to parent process (#72921)
This matches the handling added in #70997 but for the Webpack build
worker. This unifies the worker code to be the same as the one for the
static export worker which already handles this case.
When the worker exits ungracefully, we need to propagate an error signal
to the parent process so that it doesn't hang.
Fixes #67097
Closes NDX-485
Closes #67154
