Allow only (<expression>) or (<expression>, 1) for LEAD and LAG window functions as input parameters

We need to disable the third input parameter in LEAD and LAG window functions. We should support this syntax.

LEAD(<expression>) ,or LEAD(<expression>,1)
LAG(<expression>), or LAG(<expression>,1)

In both the functions above, the second parameter is the default offset value, use of any other value must he handled and reported to user as error.

Use of a third input parameter to both the functions must be disallowed.