This prevents the `disown` builtin from directly removing jobs out of
the jobs list to prevent sanity issues, as `disown` may be called within
the context of a subjob (e.g. in a function or block) in which case the
parent job might not yet be done with the reference to the child job.
Instead, a flag is set and the parser removes the job from the list only
after the entire execution chain has completed.
Closes#5720.
Directly access the job list without the intermediate job_iterator_t,
and remove functions that are ripe for abuse by modifying a local
enumeration of the same list instead of operating on the iterators
directly (e.g. proc.cpp iterates jobs, and mid-iteration calls
parser::job_remove(j) with the job (and not the iterator to the job),
causing an invisible invalidation of the pre-existing local iterators.
* Convert JOB_* enums to scoped enums
* Convert standalone job_is_* functions to member functions
* Convert standalone job_{promote, signal, continue} to member functions
* Convert standolen job_get{,_from_pid} to `job_t` static functions
* Reduce usage of JOB_* enums outside of proc.cpp by using new
`job_t::is_foo()` const helper methods instead.
This patch is only a refactor and should not change any functionality or
behavior (both observed and unobserved).
