Add `un|registered_taxonomy_for_object_type` action

[soulseekah]

To go along with registered_taxonomy and unregistered_taxonomy.

[boonebgorges]

In 43558:

Taxonomy: Introduce new hooks when registering/unregistering taxonomies for object types.

Props soulseekah.
Fixes #44733.

[mihdan]

Thanks, @soulseekah, this hook was not enough for us

[SergeyBiryukov]

Reopening for 4.9.9 consideration.

[SergeyBiryukov]

In 43631:

Docs: Update @since version for (un)registered_taxonomy_for_object_type actions introduced in [43558].

See #44733.

[SergeyBiryukov]

In 43632:

Taxonomy: Introduce new hooks when registering/unregistering taxonomies for object types.

Props soulseekah.
Merges [43558] and [43631] to the 4.9 branch.
Fixes #44733.

[pento]

[43632] needs to be reverted from the 4.9 branch, after which this ticket can be moved to the 5.0.1 milestone.

trunk will need to be updated to reflect the new version.

[boonebgorges]

In 43690:

Revert [43632] from the 4.9 branch.

These new hooks are not part of the 4.9.x scope, and will be reintroduced
as part of 5.0.x.

See #44733.

[boonebgorges]

I've reverted [43632] from the 4.9 branch. See [43690].

trunk will need to be updated to reflect the new version.

To avoid having to make the change more than once, I'll leave this ticket open, and the since param can be updated once the 5.0.1 scope is locked in.

[pento]

With 5.1 only a couple of months away, let's just do it there. The docs need updating.

[boonebgorges]

In 44321:

Update @since tag on taxonomy hooks to be introduced in 5.1.0.

The hooks were added in [43558] but pulled from the 4.9.x and 5.0.x series.

Fixes #44733.