wpLink: use the proper instance of the editor when looking at the selection. Move the email and URL regexp to variables. See #19992

git-svn-id: https://develop.svn.wordpress.org/trunk@28750 602fd350-edb4-49c9-b593-d223f7449a82
wpLink: use simpler expressions to detect email address or URL. We are not validating user input here, just suggesting.

see #19992.

git-svn-id: https://develop.svn.wordpress.org/trunk@28751 602fd350-edb4-49c9-b593-d223f7449a82
Add "edit" mode for `[embed]` and URL media previews.

See #28532.


git-svn-id: https://develop.svn.wordpress.org/trunk@28752 602fd350-edb4-49c9-b593-d223f7449a82