Make onUncaughtError and onCaughtError Configurable (#28641)

Stacked on #28627.

This makes error logging configurable using these
`createRoot`/`hydrateRoot` options:

```
onUncaughtError(error: mixed, errorInfo: {componentStack?: ?string}) => void
onCaughtError(error: mixed, errorInfo: {componentStack?: ?string, errorBoundary?: ?React.Component<any, any>}) => void
onRecoverableError(error: mixed, errorInfo: {digest?: ?string, componentStack?: ?string}) => void
```

We already have the `onRecoverableError` option since before.

Overriding these can be used to implement custom error dialogs (with
access to the `componentStack`).

It can also be used to silence caught errors when testing an error
boundary or if you prefer not getting logs for caught errors that you've
already handled in an error boundary.

I currently expose the error boundary instance but I think we should
probably remove that since it doesn't make sense for non-class error
boundaries and isn't very useful anyway. It's also unclear what it
should do when an error is rethrown from one boundary to another.

Since these are public APIs now we can implement the
ReactFiberErrorDialog forks using these options at the roots of the
builds. So I unforked those files and instead passed a custom option for
the native and www builds.

To do this I had to fork the ReactDOMLegacy file into ReactDOMRootFB
which is a duplication but that will go away as soon as the FB fork is
the only legacy root.

DiffTrain build for [a053716](a053716)

compiled/facebook-www/REVISION

@@ -1 +1 @@
-9f8daa6cb5aae476cf54611874ea7522243c6ba6
+a0537160771bafae90c6fd3154eeead2f2c903e7