3-way Diff View

The DiffEngine is now in core (Drupal 8.x) so I'm thinking changes should be done here first and then possibly back ported to Diff 7.x. Otherwise we will end up with two comparison engines in Diff 8.x or loss features when reverting back to the phpwiki version.

Closing while I see what happens with #1848264: Compare and merge PhpWiki diff*.php with MediaWiki's DairikiDiff.php and DiffEngine.php.

Note this and #1826156: Move to Text_Diff library could be reopened at some stage, particularly if someone has a lot of free time and wants to tackle these. Probably best as of Diff 8.x-4.x :)

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