Description

Since the quill-delta library uses the Apache 2 license, while Gutenberg uses the GPL 2 license there may be a problem when we PR #41 into core. This change will swap the fast-diff library for the jsdiff library, as well as port the entire quill-delta package over so as to make the swapping easier.

The jsdiff has two major differences:

• Cursor position offset: This isn't supported. It's a core feature of fast-diff, and any library that tries to implement it in a similar way needs to be using Apache 2 as well since its from the OG google library. This one is a problem for the case mentioned here. But the case mentioned in here works just fine. I've not been able to find another concrete case that's different than fast-diff.
• Trivial semantic cleanup: Same story here, though this one doesn't seem as critical as the cursor position. It just means the diff would be easier to read, rather than be wrong.

As we wait for legal's input on the licensing question, I'm leaving this in draft status as a backup plan.

The quill-delta test suite was really useful in seeing how seamless the swap could be. There was only one failure, related to the trivial semantic cleanup not existing. in that case, the end result was the same but fast-diff's result was what a human would do unlike the jsdiff one.

I'm going to keep testing it, to ensure I haven't missed any important difference.