dillon1000/react

[DevTools] Rename Fiber to Element in the Bridge Protocol and RendererInterface (#30490)

I need to start clarifying where things are really actually Fibers and
where they're not since I'm adding Server Components as a separate type
of component instance which is not backed by a Fiber.

Nothing in the front end should really know anything about what kind of
renderer implementation we're inspecting and indeed it's already not
always a "Fiber" in the legacy renderer.

We typically refer to this as a "Component Instance" but the front end
currently refers to it as an Element as it historically grew from the
browser DevTools Elements tab.

I also moved the renderer.js implementation into the `backend/fiber`
folder. These are at the same level as `backend/legacy`. This clarifies
that anything outside of this folder ideally shouldn't refer to a
"Fiber".

console.js and profilingHooks.js unfortunately use Fibers a lot which
needs further refactoring. The profiler frontend also uses the term
alot.