[jackspiva]

Adds an optional onMenuScrollToBottomOffset prop that will cause onMenuScrollToBottom to fire a certain amount of pixels before the user scrolls to the bottom fo the menu.

I think this makes the onMenuScrollToBottomProp way more useful. I am currently using this change in a fork of react-select in a work project.

My use case is that I am using onMenuScrollToBottom to load more options for the select menu. Without an offset, the user has to hit the bottom of the menu and then wait for more options to load. However, with an offset, the options can be loaded before they reach the bottom, which is a lot smoother.

Addresses #1530.

[anushaNemilidinne]

@jackspiva I am using a similar approach where if the user scrolls to the bottom of the drop down, it fetches more data from the server. But the problem is the scroll bar goes to top instead staying at the bottom. I know it's because the react component re renders on state change. But is there a way to achieve this functionality. I tried lot of different ways but no luck. Any help will be greatly appreciated! Thanks in advance!