<!--
  Note: if the issue is about documentation or the website, please file it at:
  https://github.com/reactjs/reactjs.org/issues/new
-->

**Do you want to request a *feature* or report a *bug*?**

feature

**What is the current behavior?**

When `react-dom` is loaded from CDN like `<script src="https://cdn.jsdelivr.net/npm/react-dom@16.12.0/umd/react-dom.development.js"></script>`, `react-refresh` failed to inject hook into devtools.

I've created a related issue here: https://github.com/pmmmwh/react-refresh-webpack-plugin/issues/13

We should find a way to invoke `injectIntoGlobalHook` function from `react-refresh/runtime`, however this file is in cjs format so we cannot currently do this in a simple way.

**What is the expected behavior?**

I'd like `react-refresh` to publish runtime as a umd bundle so we can reference it from CDN and put it before `react-dom`'s `<script>` element, then invoke `injectIntoGlobalHook` in the right place.

**Which versions of React, and which browser / OS are affected by this issue? Did this work in previous versions of React?**

- `react-dom`: 16.12.0
- `react-refresh`: 0.7.0
if (window.__REACT_DEVTOOLS_APPEND_COMPONENT_STACK__ !== false) {
          registerRendererWithConsole(renderer);
          patchConsole();
        }
      } catch (error) {}
    }
    
    
    const attach = target.__REACT_DEVTOOLS_ATTACH__;
    if (typeof attach === 'function') {
      const rendererInterface = attach(hook, id, renderer, target);
      hook.rendererInterfaces.set(id, rendererInterface);
    }
    hook.emit('renderer', {id, renderer, reactBuildType});
    return id;
  }
  let hasDetectedBadDCE = false;
  function sub(event, fn) {
    hook.on(event, fn);
    return () => hook.off(event, fn);
  }
  function on(event, fn) {
    if (!listeners[event]) {
      listeners[event] = [];
    }
    listeners[event].push(fn);
  }
  function off(event, fn) {