REST API: Capability check for editing a single term should use the singular form

[johnbillion]

The capability check used in WP_REST_Terms_Controller::get_item_permissions_check() is edit_terms, but it should be edit_term with the associated term ID.

The docblock description also needs correcting.

[pento]

Looks good.

I don't think it needs unit tests, short of adding tests for all combinations of singular/plural capabilities.

[nacin]

@dd32 @pento and I are discussing both this and #35614 -- and the map_meta_cap() really needs an (int) here because there's always been weird gremlins in the terms API about numeric strings being thought about as slugs.

$request['id'] is also cast to an int everywhere else in this file. I suggest we put it in both places.

[pento]

In 39464:

REST API: Capability check for editing a single term should use the singular form.

As an extra level of sanity checking, the term ID should be cast as an int in map_meta_cap().

Props johnbillion, nacin, dd32, pento.
See #35614.
Fixes #39012.

[pento]

In 39465:

REST API: Capability check for editing a single term should use the singular form.

As an extra level of sanity checking, the term ID should be cast as an int in map_meta_cap().

Merge of [39464] to the 4.7 branch.

Props johnbillion, nacin, dd32, pento.
See #35614.
Fixes #39012.