This renames the file containing the `WP_oEmbed` class to conform to the coding standards.
This commit also includes:
- A new `class-oembed.php` that includes the new file, for anyone that may've been including the file directly.
- Replaces references to the old filename with the new filename.
See #47632.
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git-svn-id: http://core.svn.wordpress.org/trunk@45474 1a063a9b-81f0-0310-95a4-ce76da25c4cd