Fix the "Uploaded to this post" filter in the "Add to gallery" state. fixes #22723

Also, use "images" wording instead of generic "media items" when in a gallery (images-only) context. fixes #22722

Both are props koopersmith

git-svn-id: https://core.svn.wordpress.org/trunk@23068 1a063a9b-81f0-0310-95a4-ce76da25c4cd