and HAVING

When calculating GROUP BY the server caches some expressions. It does
that by allocating a string slot (Item_copy_string) and assigning the 
value of the expression to it. This effectively means that the result
type of the expression can be changed from whatever it was to a string.
As this substitution takes place after the compile-time result type 
calculation for IN but before the run-time type calculations, 
it causes the type calculations in the IN function done at run time 
to get unexpected results different from what was prepared at compile time.

In the CASE ... WHEN ... THEN ... statement there was a similar problem
and it was solved by artificially adding a STRING argument to the matrix
at compile time, so if any of the arguments of the CASE function changes 
its type to a string it will still be covered by the information prepared 
at compile time.
Extended the CASE fix for cover the IN case.
An alternative way of fixing this problem is by caching the result type of 
the arguments at compile time and using the cached information at run time
instead of re-calculating the result types.
Preferred the CASE approach for uniformity and fix localization.

mysql-test/r/func_in.result:
  Bug #44399: test case
mysql-test/t/func_in.test:
  Bug #44399: test case
sql/item_cmpfunc.cc:
  Bug #44399: assume at compile time there's an extra string argument
  in the IN function (similar to CASE) to cater for possible string 
  conversions in the process of calculating the GROUP BY/aggregates.