MDEV-15957 Unexpected "Data too long" when doing CREATE..SELECT with stored func

Problems:

1. Unlike Item_field::fix_fields(),
  Item_sum_sp::fix_length_and_dec() and Item_func_sp::fix_length_and_dec()
  did not run the code which resided in adjust_max_effective_column_length(),
  therefore they did not extend max_length for the integer return data types
  from the user-specified length to the maximum length according to
  the data type capacity.

2. The code in adjust_max_effective_column_length() was not correct
   for TEXT data, because Field_blob::max_display_length()
   multiplies to mbmaxlen. So TEXT variants were unintentionally
   promoted to the next longer data type for multi-byte character
   sets: TINYTEXT->TEXT, TEXT->MEDIUMTEXT, MEDIUMTEXT->LONGTEXT.

3. Item_sum_sp::create_table_field_from_handler()
   Item_func_sp::create_table_field_from_handler()
   erroneously called tmp_table_field_from_field_type(),
   which converted VARCHAR(>512) to TEXT variants.
   So "CREATE..SELECT spfunc()" erroneously converted
   VARCHAR to TEXT. This was wrong, because stored
   functions have explicitly declared data types,
   which should be preserved.

Solution:

- Removing Type_std_attributes(const Field *)
  and using instead Type_std_attributes::set() in combination
  with field->type_str_attributes() all around the code, e.g.:
     Type_std_attributes::set(field->type_std_attributes())

  These two ways of copying attributes from a Field
  to an Item duplicated each other, and were slightly
  different in how to mix max_length and mbmaxlen.

- Removing adjust_max_effective_column_length() and
  fixing Field::type_std_attributes() to do all necessary
  type-specific calculations , so no further adjustments
  is needed.
  Field::type_std_attributes() is now called from all affected methods:
   Item_field::fix_fields()
   Item_sum_sp::fix_length_and_dec()
   Item_func_sp::fix_length_and_dec()
  This fixes the problem N1.

- Making Field::type_std_attributes() virtual, to make
  sure that type-specific adjustments a properly done
  by individual Field_xxx classes. Implementing
  Field_blob::type_std_attributes() in the way that
  no TEXT promotion is done.
  This fixes the problem N2.

- Fixing Item_sum_sp::create_table_field_from_handler()
  Item_func_sp::create_table_field_from_handler() to
  call create_table_field_from_handler() instead of
  tmp_table_field_from_field_type() to avoid
  VARCHAR->TEXT conversion on "CREATE..SELECT spfunc()".

- Recording mysql-test/suite/compat/oracle/r/sp-param.result
  as "CREATE..SELECT spfunc()" now correctly
  preserve the data type as specified in the RETURNS clause.

- Adding new tests

1 files changed, 4 insertions, 0 deletions

diff --git a/sql/item_sum.h b/sql/item_sum.h
index 1ed3d870bcc..ea8b2f149df 100644
--- a/sql/item_sum.h
+++ b/sql/item_sum.h
@@ -1297,6 +1297,10 @@ public:
   {
     return SP_AGGREGATE_FUNC;
   }
+  Field *create_field_for_create_select(TABLE *table)
+  {
+    return create_table_field_from_handler(table);
+  }
   void fix_length_and_dec();
   bool fix_fields(THD *thd, Item **ref);
   const char *func_name() const;