When reporting an error about unresolvable annotation attribute, use the position of the explicit left-hand-side of the assignment if available, otherwise use the position of the right-hand-side.
Reviewed-by: jfranck
8019421: Javac doesn't fill in end position for some annotation related errors
8019422: Javac doesn't fill in end position for uninitialized variable errors
Reviewed-by: jjg, mcimadamore
