Fix zed sometimes stopping by using setsid on interactive shells (#29070)

For some reason `SIGTTIN` sometimes gets sent to the process group,
causing it to stop when run from a terminal. This solves that issue by
putting the shell in a new session + progress group.

This allows removal of a workaround of using `exit 0;` to restore
handling of ctrl-c after exit. In testing this appears to no longer be
necessary.

Closes #27716

Release Notes:

- Fixed Zed sometimes becoming a stopped background process when run
from a terminal.

crates/vim/Cargo.toml

@@ -28,7 +28,6 @@ futures.workspace = true
 gpui.workspace = true
 itertools.workspace = true
 language.workspace = true
-libc.workspace = true
 log.workspace = true
 multi_buffer.workspace = true
 nvim-rs = { git = "https://github.com/KillTheMule/nvim-rs", branch = "master", features = ["use_tokio"], optional = true }