wpView:
- Don't wrap single-line URLs in [embed]. Use them directly in generating a view.
- If the embedding HTML contains a script, "sandbox" it in an iframe to prevent it from changing the editor DOM.
- Automatically add toolbar and overlay when needed.
- Try to embed single-line URLs only if they are pasted in an empty paragraph.
Props avryl, see #28195

git-svn-id: https://develop.svn.wordpress.org/trunk@28748 602fd350-edb4-49c9-b593-d223f7449a82