In accurate scrollBarWidth for inner scroll view when the document scroll bar width is modified.

[TotooriaHyperion]

We are using Eclipse theia, and it has a custom scroll bar style.
And we need a virtual scroll view inside it with overflow: overlay, which is no longer supported by Chrome.
I think allowing the user to pass in scrollbarWidth by props can fix this.
Because not all scroll view has the same scroll bar width.