Fix onScrollbarPresenceChange not invoking at correct timing

[NoyChan]

Hi
I noticed that the calculation of verticalScrollBarSize does not consider the current horizontalScrollBarSize, and vice versa, which lead to incorrect invoke timing of onScrollbarPresenceChange, as shown below

after adding this._horizontalScrollBarSize and this._verticalScrollBarSize, it work normal

[bvaughn]

Sorry for the very long delay in getting back to you about this!

I've just finished a large update for version 10 of react-virtualized (#1900): the library has been rewritten in TypeScript, every component is now a function component (React 18+ is required), and the source moved from source/ to lib/. Because of that, this PR can't be merged as-is. Version 10's Grid still checks each scrollbar's presence independently, so onScrollbarPresenceChange can still fire at the wrong time.

If you're still interested in this change, I'd welcome a new PR with it rebased onto the version-10 branch (or onto master once version 10 has been merged).