Add a function, `get_comments_number_text()`, that returns instead of echoing. `comments_number()` wraps it.

Props kapeels, nbachiyski.
Fixes #10177.

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Allow comments in the trash to marked as spam.

Props mordauk.
Fixes #19256.

Built from https://develop.svn.wordpress.org/trunk@28913


git-svn-id: http://core.svn.wordpress.org/trunk@28712 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Revert [28911] for performance concerns.

See #14157.

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git-svn-id: http://core.svn.wordpress.org/trunk@28713 1a063a9b-81f0-0310-95a4-ce76da25c4cd