Problem: the highlight-yank plugin exmaple provided in the doc behaves
incorrectly when selection is set to exclusive.
Solution: use a unified offset of 1 and pass 'exclusive: false' to
getregionpos(), while at it, also clarify when the
TextYankPost autocommand triggers.
closes: #16866
Signed-off-by: Jim Zhou <jimzhouzzy@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>