Use clone3 / CLONE_INTO_CGROUP to have the Linux kernel create the process in the
correct cgroup rather than move the process into the cgroup after it is created.
For now, bash integration must be explicitly enabled (by setting
`shell-integration = bash`). Our automatic shell integration requires
bash version 4 or later, and systems like macOS continue to ship bash
version 3 by default. This approach avoids the cost of performing a
runtime version check.
Fish automatic integration taken as an example.
Just like fish, Elvish checks `XDG_DATA_DIRS` for its modules.
Thus, Fish integration in zig is reused, and integration in
Elvish now removes `GHOSTTY_FISH_XDG_DIR` environment variable
on launch.
When the -c option is present, then commands are read from the first
non-option argument command string. Our simple implementation assumes
that if we see at least the '-c' option, a command string was given, and
the shell is always considered to be non-interactive - even if the '-i'
(interactive) option is also given.
bash reads HISTFILE at startup to locate its history file, but this is
apparently too early for it to be able to expand home-relative paths. We
now manually expand the full path and add that to the environment.
This change adds automatic bash shell detection and integration.
Unlike our other shell integrations, bash doesn't provide a built-in
mechanism for injecting our ghostty.bash script into the new shell
environment.
Instead, we start bash in POSIX mode and use the ENV environment
variable to load our integration script, and the rest of the bash
startup sequence becomes the responsibility of our script to emulate
(along with disabling POSIX mode).
