cursor reinstated at end of P after unwrap

[meremagee]

logged that the cursor is lost on unwrap in editor repo: https://github.com/Automattic/editor/issues/509, but wanted to note that cursor is reset at the end of the P when you start typing again after it's lost. It should persist where you were before unwrap.

repro

• type or paste in text
• add cursor anywhere within the text - on a space, mid-word, etc
• use keyboard or icon to set bold
• type
• use keyboard or icon to unset bold
• cursor is no longer visible
• type and cursor reappears at end of text

https://cloudup.com/cZPuk_GtjGZ

todo from @TooTallNate - https://github.com/webmodules/unwrap-range/blob/master/index.js#L102-L114