Move fix_rows functions to helper module

[JGuetschow]

Several country reading script contain a fix_rows function to combine rows split up in the pdf reading process (because they contained line breaks in some cells). Make one unified function and place that in the helper module to reduce code and possible confusion.

Submissions that where the fix_rows function is used are:

• Mexico BUR3,
• Taiwan 2022 NIR

Additional submission where the code is not integrated into the repository use the function

[JGuetschow]

The function is now available in the the helper module but might need modifications to work with all use cases.