DevTools: Profiling tool improvements umbrella

I met with @lahmatiy this afternoon to chat about his project [react-render-tracker](https://github.com/lahmatiy/react-render-tracker). Here are a few pain points mentioned during the meeting: * Not clear when a component/tree is unmounted/remounted. * DevTools typically displays data for a component in current update (e.g. the latest) but doesn't represent changes over time. * It isn't always clear why something updates (e.g. why did context change higher up, what was the flow of props/state above that resulted in a new prop) * It's difficult to detect when effects re-run unexpectedly due to dependency problems. (Nothing really reports this.) This is an umbrella issue for some ideas I wrote down during the discussion that might be good additions to the React DevTools/Profiler. The items listed below may be worked on independently– and some may turn out to be not worth doing (but they seem worth discussing and considering). ## Legacy profiler ### Track changed values The Profiler currently has an opt-in setting for detecting _why_ something re-rendered, but all this does is show the name of the state/prop that changed. Should we also add a setting to display the changed value? We shied away from doing this for a long time because: * We didn't want to incur the cost of serializing deep object structures during a profiling session. * Without eagerly serializing an object, we don't have a solution for mutable values. (We can't serialize these later since they may have changed.) Maybe there are some ways to address the above concerns though? For instance, we could reduce the amount of data we needed to eagerly serialize by: * Only serialize values that _changed_ between renders. (This would avoid the mutable object scenario.) * Only serialize _parts_ of an object that changed. (See [here](https://github.com/lahmatiy/react-render-tracker/blob/39d598aaa12274cb8a015dacf55b68687bde7d8d/src/publisher/react-integration/devtools-hook-handlers.ts#L356-L374) for possible precede…