Unit Tests: The `assertEqualSets()` helper was returning true for some sets that were not equal. `assertEqualSets()` now behaves correctly, and the new `assertEqualSetsWithIndex()` helper also checks that the array indexes are the same.

Fixes #30522.

Built from https://develop.svn.wordpress.org/trunk@30687


git-svn-id: http://core.svn.wordpress.org/trunk@30677 1a063a9b-81f0-0310-95a4-ce76da25c4cd