Tests: Add unit tests for object_ids handling in WP_Term_Query

[himanshupathak95]

Trac ticket: https://core.trac.wordpress.org/ticket/63256

Adds unit test coverage for the fix implemented in #8668 that addresses unnecessary array_map() processing in WP_Term_Query::get_terms() when object_ids is not set.

This PR -

• Verifies that when object_ids is null (default), all terms are returned without filtering
• Ensures the optimization skips unnecessary array_map() processing
• Validates that numeric zero (0) is treated as a valid object ID
• Prevents regression where 0 might be incorrectly treated as empty

Testing

npm run test:php -- --filter=Tests_Term_Query

Follows the patch of #8668 by @dilipbheda

Props: @dilipbheda for the original patch

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Props abcd95, westonruter.

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[westonruter]

I've added 3d7f52a to account for the case for when someone may have supplied 'object_ids' => false. This will now preserve the original behavior of returning no terms. The same tests pass in trunk as in this branch.

[westonruter]

Alas, the Tests_Term_getTerms::test_cache_key_generation test is now failing with the data set "array object_ids vs string object_ids".