HTML: Exit mirror mode when going to new line

[octref]

Currently, the logic for exiting mirror mode is when the text before/after primary/second cursors do not match any more.

One caveat is:

    // some spaces
<|div>
    // some spaces
</|div>
    // some spaces

Press up/down, it will keep the multi cursors.

When you press up/down, HTML should always exit mirror-cursor. If your primary cursor lands on another tag's name it should reenter mirror-cursor.