[BUG] "Grouped" options breaks screen readers

Using the "grouped" feature breaks screen readers.

Because group sub-component elements exist as the first item underneath menuList; aria readers will think that the dropdown list contains however many group elements there are, NOT however many option items there are, like it should.

To reproduce

1. Navigate to the "Grouped" example on the main react-select homepage: https://react-select.com/home
   
2. Focus the grouped example element with NVDA (or JAWS) enabled.
3. Click spacebar to open the menu.
4. Click down the the keyboard arrow keys until the option "Purple" is selected.
5. Screen-reader will call out that the element is in position "0 of 2" despite the fact that there are 14 items in the list and purple is the third member of that list; it should read "3 of 14".

It's saying 0 of 2 because it's counting the number of group elements under menuList (Colors and Flavors), not the Options nested further down inside Group.

Note> Adding role="presentation" to group may fix this issue.

Start at the grouped select implementation, especially the Group and menuList elements, and reproduce the issue from the Grouped example on react-select.com/home with NVDA or JAWS. Verify that the grouped options are exposed as one list and that selecting Purple is announced as 3 of 14 rather than 0 of 2.