dillon1000/react

[flow] Upgrade Flow to 0.245.2 (#30919)

## Summary

This PR bumps Flow all the way to the latest 0.245.2. 

Most of the suppressions comes from Flow v0.239.0's change to include
undefined in the return of `Array.pop`.

I also enabled `react.custom_jsx_typing=true` and added custom jsx
typing to match the old behavior that `React.createElement` is
effectively any typed. This is necessary since various builtin
components like `React.Fragment` is actually symbol in the React repo
instead of `React.AbstractComponent<...>`. It can be made more accurate
by customizing the `React$CustomJSXFactory` type, but I will leave it to
the React team to decide.

## How did you test this change?

`yarn flow` for all the renderers