Add some unit tests for `is_object_in_term()`.

These tests check a number of the ways that different kinds of values for
`$terms` (integers that match term_id, strings that match term_id or name or
slug) are handled.

See #29467.

git-svn-id: https://develop.svn.wordpress.org/trunk@30204 602fd350-edb4-49c9-b593-d223f7449a82
In `in_object_in_term()`, only check numeric string values against term_id.

The previous `in_array()` check was playing too loose with mixed types, such
that a string like '10_term_name' would incorrectly match a term_id 10.

Props nobinobi, realloc.
Fixes #29467.

git-svn-id: https://develop.svn.wordpress.org/trunk@30205 602fd350-edb4-49c9-b593-d223f7449a82