Docs: Use third-person singular verbs in DocBlock summaries for the...

Docs: Use third-person singular verbs in DocBlock summaries for the `WP_Site_Logo` class, introduced in [36698].

Also minorly improves various inline docs.

See #33755. See #35986.

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git-svn-id: https://core.svn.wordpress.org/trunk@36787 1a063a9b-81f0-0310-95a4-ce76da25c4cd