devtools: Implement object and function property preview

[atbrakhi]

Implement property preview for the debugger popup. When hovering over variables while paused at a breakpoint, users can now see object properties and function metadata

Testing: Current tests are passing. Manual testing.
Fixes: Part of #36027

[atbrakhi]

@eerii I couldn’t make it any shorter. It is complicated. Everything is tightly coupled, and when I tried to split it into separate PRs, it only became more complex and confusing. There’s a lot going on here, but the good thing is it’s mostly limited to functions and objects, other parts are untouched.

I also had arguments support in this PR, but I removed it because it was making change bigger. It’s better to land this first, and then I’ll send another PR for showing arguments in the preview.

I’ve tried to keep the implementation close to Firefox, while also keeping in mind that we’ll be adding more features in the future. That does mean some extra code in debugger.js, for example parts of this could have been simpler or even in the same function. But since we’ll be building on this, I decided to lay a foundation for future work. We can now implement on top of this.

I’ve documented things as much as I could, but I’m also happy to walk you through the changes on a call. Let me know!

[eerii]

Most comments are for followups, the rest looks great! :)