body_class docblock parameter description incorrect

[JPry]

For the body_class filter, the $class variable is described as a string when in fact it is an array.

[JPry]

Fix body_class docblock

[SergeyBiryukov]

In 35398:

Docs: Correct $class parameter type and description for body_class filter.

Props JPry.
Fixes #34452.

[SergeyBiryukov]

In 35399:

In get_post_class(), ensure that we always coerce the class list passed to the function to an array, even when it's empty.

This is consistent with get_body_class(), see [18176].

See #34452.

[SergeyBiryukov]

In 35400:

Docs: After [35399], correct $class parameter type and description for post_class filter.

See #34452.