docs: initial docs for Performance tracks

[hoxyq]

Adds initial docs for React Performance tracks.

These docs cover only client-side tracks for now: Scheduler and Components.

[github-actions]

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[rubennorte]

Suggested change

	title: React Performance tracks
	title: React performance tracks

It feels weird to capitalize performance. I'd either capitalize everything or just React. There are other examples of this in the doc.

[hoxyq]

My thinking is, Performance is capitalized here to align with "Performance panel" in the browser.

@rickhanlonii How do you feel about the naming?

[rubennorte]

We should mention that not all components rendered are shown here. Only the ones taking more than a specific amount of time.

[hoxyq]

Good point, added a note:

<Note>
Unlike renders, not all effects are shown on the Components track by default.
To maintain performance and prevent UI clutter, React will only display those effects, which had a duration of 0.05ms or longer, or triggered an update.
</Note>

I am working on a feature that will record effects that triggered an update, independent of their duration

[rubennorte]

Regarding that note, are we showing all components rendered, but not all effects, or are we also not showing all the renders?

[hoxyq]

All renders are showed, independent from their corresponding duration.

Not all effects are showed. With react/react#34648, we won't show the ones that took 0.05ms or less and didn't trigger any blocking updates.

[rubennorte]

State updates from commits (layout effects, ref assignments, etc.) are also scheduled with a blocking priority. We should probably mention that too.

[hoxyq]

The "The synchronous updates" are referring to the application updates, not to the state updates.

I am not sure how to update it to clarify it more

[eps1lon]

Do we have a concrete example we can link to instead? Maybe even with a backlink telling people to use the profiler to spot cascading updates?

[hoxyq]

We don't have a section that explains fully the cascading updates. Only a small paragraph on https://react.dev/learn/you-might-not-need-an-effect#updating-state-based-on-props-or-state, where it is briefly mentioned.

That's a great idea for a separate task, we could add a section to it that explains how cascading updates could be spotted with Performance tracks. Will follow up.