The start/end/"preferred" positions for the JCMemberReference needs to be updated. The current state has several problems:
-member references does not have handling in TreeInfo.getStartPos, and so the starting position of the MemberRef with annotated expression is inside the MemberRef's 'expr'. This causes TreePosTest failures.
-the "preferred" .pos of the MemberRef should point to the '::'.
-the end pos set to the MemberRef's expr when the expr is an annotated type is wrong (the annotated expr spans to the end of the MemberRef).