After previous commits, we can drop entire task's state and replace it
with single boolean flag, which determines if a task was aborted.
Once a task was aborted, it cannot get resurrected to a normal state.
If the view building coordinator is running, adjust view_building_tasks
in case of tablet operations.
The mutations are generated in the same batch as tablet mutations.
At the start of tablet migration/resize/RF change, started
view building tasks are aborted (by setting ABORTED state) if needed.
Then, new adjusted tasks are created in group0 batch which ends the
tablet operation and aborted tasks are removed from the table.
In case the tablet operation fails or is revoked, aborted view building
tasks are rollback by creating new copies of them and aborted ones are
deleted from the table.
View building tasks are not aborted/changed during tablet repair,
because in this case, even if vb task is started, a staging sstable will
be generated.
