Config contains the command, working directory, and environment
variables intended to be passed to the new split, but it looks like we
forgot to include it as an argument in this branch.
Discussion: https://github.com/ghostty-org/ghostty/discussions/8637
Fixes#7647
See #7647 for context. This commit works by extending the `input` work
introduced in #7652 to libghostty so that the macOS can take advantage
of it. At that point, its just the macOS utilizing `input` in order to
set the command and `exit` up similar to Terminal and iTerm2.
