patch 9.1.0261: Vim9: protected class and funcrefs accessible outside the class

patch 9.1.0261: Vim9: protected class and funcrefs accessible outside the class

Problem:  Vim9: protected class and funcrefs accessible outside the class
          (Aliaksei Budavei)
Solution: Check if class and object funcrefs are protected
          (Yegappan)

closes: #14407

Signed-off-by: Yegappan Lakshmanan <yegappan@yahoo.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>