Add a note explaining when the has_many associations callbacks will be called or not.

This PR addresses the issue described in #28025. On `dependent: :nullify` strategy only the foreign key of the relation is nullified. However on polymorphic associations the  `*_type` column is not nullified leaving the record with a NULL `*_id` but the `*_type` column is present.

I was puzzled about why `collection=` was destroying the removed
records on an association with `dependent: :destroy`, even after
consulting the documentation for that option.  I had to dive into the
Active Record source to understand what was going on: eventually
`collection=` calls `collection.delete` on the ousted records, and it
also uses the `:dependent` option to decide how to remove records.

It would have helped me to have mention of this in the documentation for
`:dependent`, not just under `collection.delete` (which I found much
later).

Briefly mention the broader impacts of `:dependent` in the Association
Basics guide.

[ci skip]

This commit removes the dependent: :destroy option from the belong_to example since there is a warning associated with the usage of dependent: :destroy along with belongs_to. Based on the feedback on the issue #33914, I  replaced dependent: :destroy with touch: :books_updated_at which will make the example consistent with the example that already exists on that page.
 * Also Removing the touch option from the belong_to scopes example as the option doesnt have any relation to association scope.

Follow up #32146.

Line items are a holdover from when orders were used in the examples
instead of books.

http links will be redirected to the https version, but still better to
just directly link to the https version.

Revert "Merge pull request #33385 from lanzhiheng/add-example-for-has-and-belongs-to-many-association"

This reverts commit 3c8c4100, reversing
changes made to daee94da.

We have this information below in the reference section for
has_and_belongs_to_many.

[ci skip] A regular expression was used to find a lot of missing Oxford
commas and add them.  The regular expression was as follows.

", ([a-zA-Z0-9.\`:'\"]+ ){1,6}(or|and) "

Updated the method counts and unified them all on numerals.

[ci skip] setting :inverse_of works with :as, :through and :polymorphic options, and is needed for bi-directionality with a scope

[ci skip] Remove :conditions opion from association basics guide

This got replaced by scopes.

  - Make all `ActiveRecord::Base.find` as link
  - Remove redundant sentences
    "It also adds the additional condition that the object must be in the collection."

This reverts commits 5147ab12 and 391043ab.

These commits looked to intend to change documents of has_many dependent options, but actually changed documents of belongs_to dependent options.

passing `unique` parameter to belongs_to not right,

Rails automatically finds bi-directional associations between models
with well-named associations. However, when using non-standard naming,
you have to use :inverse_of to explicitly tell Rails about the bi-
directional association.

With reference to #27516

[ci skip]

Because I can never remember if `collection_singular_ids=` persists
or not (it does).

[ci skip]

Passing `true` to the association has been deprecated.

Clarifies the documentation here to mean all options are for when the
relation is destroyed; also now reflects the documentation on this same
option found in the has_one section.