Introduce Edit Image (single mode) in the media modal and use it to edit...

Introduce Edit Image (single mode) in the media modal and use it to edit images inserted in the editor. Adds new feature: replace an image in the editor. Props gcorne, see #24409.
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git-svn-id: https://core.svn.wordpress.org/trunk@26924 1a063a9b-81f0-0310-95a4-ce76da25c4cd