Code fix to adjust n-tuples

[psfinaki]

Originally suggested by @T-Gro

When pattern matching a DU member on a big n-tuple (e.g. 5 items) and n decreases because of a change - you get a type mismatch because a 5-tuple does not work with a 6-tuple.

The codefix could:

• Add one more " , _ ,"
• BETTER: suggest to convert the DU member matching from positional arguments to named ones.
  • Precondition: The items of the DU member have real names, and not just Item1..ItemN
    • All the discarded _ ones can be ignored
    • Only the really used ones remain

This would react on: FS0727 - This union case expects %i arguments