Change popover auto right placement to use container right offset 

When using "auto right" as the placement for a popover, the auto placement code uses the container width instead of the right offset of the container to determine whether to use left or right placement. If the container has anything but zero for a left offset, this can result in incorrect usage of left placement when there is plenty of room for right placement.

Changed to compare the right offset of the container instead of the container width.

Fixes #15367