Function position Enhances with Optional start_pos Argument

Why it matters

This enhancement allows users to specify the starting position within the string from which to begin the search, providing more control and flexibility in substring search operations.

How to use it

To use the new feature, call the position function with the additional start_pos parameter, for example: position(haystack, needle, start_pos), where start_pos is the position to start searching from inside the string.