Add Function Alias For MOD/TRUNCT/POSITION

We already have the impl of the following functions. We can add the function alias to be consistent with ANSI.

 
MOD(<m>,<n>)

Returns the remainder of m divided by n. Returns m if n is 0.

 
TRUNC

Returns the number x, truncated to D decimals. If D is 0, the result will have no decimal point or fractional part. If D is negative, the number is zeroed out.

 
POSITION

Returns the position of the char IN <string>) in the source string.