WL#4448: Generalize the handlerton::fill_files_table call with handlerton::fill_is_table

Generalize the handlerton::fill_files_table call with
handlerton::fill_is_table that passes an id of the information 
schema table to be populated.

we want to add support for other I_S tables and do not want to 
modify the handlerton every time for every new table. Besides, 
these function would supposedly share a lot of common code.