When deleting associated records, Rails loads all associations into memory
(https://github.com/rails/rails/issues/22510) before destroying them. This
can cause a surge in memory and cause destruction of objects to fail
due to idle in transaction database timeouts. This fix is inspired from
https://github.com/thisismydesign to destroy `has_many` relationships
in batches.

Closes #44610

We request Gitaly in a N+1 manner to build discussion diffs. Once the diffs are from different revisions, it's hard to make a single request to the service in order to build the whole response.
With this change we solve this problem and simplify a lot fetching this piece of info.

This can occur when a note is added to a commit and then this commit
is deleted.

Signed-off-by: NRémy Coutable <remy@rymai.me>

This reverts commit 2ebafdfb

This reverts commit 4e1bb1d1.

destroy_all loads all records at once

ObjectStore uploader requires presence of associated `uploads` record
when deleting the upload file (through the carrierwave's after_commit
hook) because we keep info whether file is LOCAL or REMOTE in `upload`
object.

For this reason we can not destroy uploads as "dependent: :destroy" hook
because these would be deleted too soon. Instead we rely on
carrierwave's hook to destroy `uploads` in after_commit hook.

But in before_destroy hook we still have to delete not-mounted uploads
(which don't use carrierwave's destroy hook). This has to be done in
before_Destroy instead of after_commit because `FileUpload` requires
existence of model's object on destroy action.

This is not ideal state of things, in a next step we should investigate
how to unify model dependencies so we can use same workflow for all
uploads.

Related to #45425

In Rails 5.0 automatic inverse does not work for polymorphic relathionships.
It was fixed in Rails 5.2: https://github.com/rails/rails/pull/28808

Until that the `inverse_of: :source` argument should be set explicitly.

Introduce `use_fast_destroy` helper for parent associations.  Rename method names in build_trace_chunks. Forbid `destroy` method when `FastDestroyAll` included.

Direct disk access is done through Gitaly now, so the legacy path was
deprecated. This path was used in Gitlab::Shell however. This required
the refactoring in this commit.

Added is the removal of direct path access on the project model, as that
lookup wasn't needed anymore is most cases.

Closes https://gitlab.com/gitlab-org/gitaly/issues/1111