This allows running `set` without triggering any event handlers.
That is useful, for example, if you want to set a variable in an event
handler for that variable - we could do it, for example, in the
fish_user_path or fish_key_bindings handlers.
This is something the `block` builtin was supposed to be for, but it
never really worked because it only allows suppressing the event for
the duration, they would fire later. See #9030.
Because it is possible to abuse this, we only have a long-option so
that people see what is up.
[w]open_dir does not pass O_CREAT, so the mode argument to open is never used.
also, O_CREAT | O_DIRECTORY could not be used (portably) to create a directory.
(on POSIX does not specify what should happen, on Linux it is EINVAL.)
Remove the last non scoped place where we disable protocols (just before
exec(1)); it's not necessary with the current approach because we always
disable inside eval.
There is an edge case where we don't:
fish -ic "exec bash"
leaving bash with CSI u enabled. Disable that also in -ic mode where we
don't have a reader.
In future we should use the same approach for restore_term_mode() but I'm
not sure which one is better.
This is resistant to misuse by including O_DIRECTORY in the open flags and it is
a separate function from {w,}open_cloexec() in preparation for making that one
return a `File` instead of an `OwnedFd`.
