When calling `register_rest_route()`, the `args` parameter for a route should be an array of arrays. However, some plugins/themes have passed an array of strings or key-value pairs which produces a PHP warning when `array_intersect_key` is used to filter the array keys based on an allowed list of schema keywords.
This change adds a check of the `args` parameter to ensure it's an array of arrays, presenting a `_doing_it_wrong` if any element of `args` is not an array and restructuring to an array of arrays. This change also adds a unit test for the incorrect usage described above, expecting that a `_doing_it_wrong` is produced.
Props slaFFik, desrosj, apermo, AndrewNZ, aristath, poena, dovyp, timothyblynjacobs, Hinjiriyo, johnmark8080, nateallen.
Fixes#51986.
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git-svn-id: http://core.svn.wordpress.org/trunk@53898 1a063a9b-81f0-0310-95a4-ce76da25c4cd
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