Refactor ProfilerContext to use reducer instead of multi-state

[bvaughn]

The ProfilerContext is currently comprised of several pieces of related state, each managed with useState. This necessitates awkward checks like this or even worse like this or this.

This context should be refactored to use a single reducer (useReducer) like TreeContext. This is a bit more involved at the moment because of suspense and the ProfilerContext being higher level than the suspense cache. Although maybe we could work around this by using some sort of subscription?

See related issues like #16441 and commit 4697f5b.