Convert lib-3rd-party/dynamic-contrast.js to typescript

[silverneko]

Hi,

First of all, thanks for this awesome extension!

I'm working on porting this extension to our in house editor. My company, Google, has a editor based on the web-based vscode. I'm currently having some difficulties because this extension have a mixture of .js and .ts source. Our build system doesn't like that and I'm having a hard time integrating the code.

Instead of fiddling with our build system and hack around the issues, I'd like to just rewrite the entire lib-3rd-party/dynamic-contrast.js to .ts, as that would make the codebase of this extension purely typescript.

For me, this change would make integrating this project with our repository simpler.
For you, this change shouldn't have any meaningful affect, other than added type safety as dynamic-contrast would now be properly typed.