Refactored backend renderer to remove most of the recursion

[bvaughn]

DevTools doesn't currently handle extremely deep trees (#16491) or extremely wide trees (#16501) very well, due to recursion in the backend interface. This PR removes most of that.

As a sanity test, I confirmed that after this refactor, DevTools was able to handle the following:

const Child = ({ children = null }) => children;

const Deep = () => {
  let children = null;
  for (let i = 0; i < 15000; i++) {
    children = <Child>{children}</Child>;
  }
  return children;
};

const Wide = () => {
  let children = [];
  for (let i = 0; i < 15000; i++) {
    children.push(<Child key={i} />);
  }
  return children;
};

Migrated from bvaughn/react-devtools-experimental#385

[sizebot]

No significant bundle size changes to report.

Generated by 🚫 dangerJS against b8e1f81

[bvaughn]

This method needs to be migrated too, but it's not going to be as straight forward as the other two since it depends on its own recursive return value.

[bvaughn]

We may want to do this eventually but I'm going to close for now.