Coding Standards: Use strict comparison where static strings are involved.

This reduces the number of `WordPress.PHP.StrictComparisons.LooseComparison` issues in half, from 1897 to 890.

Includes minor code layout fixes for better readability.

See #49542.
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git-svn-id: https://core.svn.wordpress.org/trunk@47584 1a063a9b-81f0-0310-95a4-ce76da25c4cd