[DevTools] Remove markers from Suspense timeline

[eps1lon]

The marker were intended so that you can click on the "meaningful" milestones. But there's just too many in a sufficiently large app resulting in collapsed markers. We could make the input scrollable though for now I prefer having the whole timeline hoverable at once.

Maybe there's a better heuristic like "biggest N" boundaries instead. For now I added X / N display for orientation like we have in the Profiler tab.

Before

After:

[hoxyq]

nit: the vertical alignment feels a bit off

[eps1lon]

Yeah, it's aligned with the slider thumb but not track. The slider is just the default input[type="range"] but that's not the final version. Just gives me keyboard and pointer interactions out-of-the-box.

[sebmarkbage]

Maybe just turn it into a big red box saying "You have too many boundaries. This is never good design.".

[sebmarkbage]

Feels awkward to optimize for the case you shouldn't be in and where it becomes hard to use the tool for anything useful anyway.

Btw, are you filtering out on hasUniqueSuspenders yet? That seems like something that's needed as the first thing.

[sebmarkbage]

Another milestone would be the change in environment. That was the only thing we intended originally to flag. E.g. "Prerender".