Convert diff match patch to typescript

[rgbkrk]

I posted in google/diff-match-patch to see if they'd be open to a Typescript version (ref google/diff-match-patch#58)

Right now I'm working with a vendorized copy of diff-match-patch as part of CoCalc's code base. I'm considering converting diff-match-patch to typescript as the rest of cocalc's repository is switching over to typescript.

However, I view the source of truth for the implementation to be here in this repository (just like the npm package for diff-match-patch from @JackuB et. al. defers to here). Instead of modifying it "internally", I'd like to contribute upstream here.

I would assume we'd still make the compile target match what's documented in the wiki:

it works in Netscape 4, Internet Explorer 5.5, and all browsers released since the year 2000

As part of this, I'd keep it closely aligned with @types/diff-match-patch.

Response from @NeilFraser:

Hi Kyle,

Yes, we would be interested in a TypeScript version. It would solve a lot of problems with trying to shoehorn the JS version into TS applications while keeping various type checkers happy.

I worked on a TS version a few months ago, and made considerable progress. However, other things got in the way, and I had to put it to one side. It also became apparent to me that I'm the wrong person to make design decisions in TS since I have no expertise in this language. Here's what I have so far, maybe it would be a good starting point: https://neil.fraser.name/temp/typescript.zip

Prior to moving our vendorized copy into this new library, I'm going to contribute to google/diff-match-patch and keep folks updated here.