MDEV-12588 Add Type_handler::type_handler_for_tmp_table() and Type_handler::type_handler_for_union()

1. Implementing the task according to the description:

a. Adding Type_handler::type_handler_for_tmp_table().
b. Adding Type_handler::type_handler_for_union_table.
c. Adding helper methods Type_handler::varstring_type_handler(const Item*),
   Type_handler::blob_type_handler(const Item*)
d. Removing Item::make_string_field() and
   Item_func_group_concat::make_string_field().
   They are not needed any more.
e. Simplifying Item::tmp_table_field_from_field_type() to just two lines.
f. Renaming Item_type_holder::make_field_by_type() and implementing
   virtual Item_type_holder::create_tmp_field() instead.
   The new implementation is also as simple as two lines.
g. Adding a new virtual method Type_all_attributes::get_typelib(),
   to access to TYPELIB definitions for ENUM and SET columns.
h. Simplifying the code branch for TIME_RESULT, DECIMAL_RESULT, STRING_RESULT
   in Item::create_tmp_field(). It's now just one line.
i. Implementing Type_handler_enum::make_table_field() and
   Type_handler_set::make_table_field().

2. Code simplification in Field_str constructor calls.

a. Changing the "CHARSET_INFO *cs" argument in constuctors for Field_str
   and its descendants to "const DTCollation &collation". This is to
   avoid two step initialization:
   - setting Field_str::derivation and Field_str::repertoire to the
     default values first
   - then resetting them using:
     set_derivation(item->derivation, item->repertoire).

b. Removing Field::set_derivation()

c. Adding a new constructor DTCollation(CHARSET_INFO *cs),
   for the old code compatibility.

3. Changes in test results

As a side effect some test results have changed, because
in the old version Item::make_string_field() converted
TINYBLOB to VARCHAR(255). Now TINYBLOB is preserved.

a. sp-row.result
   This query:
     CREATE TABLE t1 AS SELECT tinyblob_sp_variable;
   Now preserves TINYBLOB as the data type.
   Before the patch a VARCHAR(255) was created.

b. gis-debug.result
   This is a debug test, to make sure that + and - operators
   are commutative and non-commutative correspondingly.
   The exact data type is not really important.
   (But anyway, it now chooses a better data type that fits the result)

mysql-test/suite/compat/oracle/r/sp-row.result

@@ -2129,8 +2129,8 @@ CALL p1();
 SHOW CREATE TABLE t1;
 Table	Create Table
 t1	CREATE TABLE "t1" (
-  "var" varchar(255) DEFAULT NULL,
-  "rec.var" varchar(255) DEFAULT NULL
+  "var" tinytext DEFAULT NULL,
+  "rec.var" tinytext DEFAULT NULL
 )
 DROP TABLE t1;
 DROP PROCEDURE p1;
@@ -2169,8 +2169,8 @@ CALL p1();
 SHOW CREATE TABLE t1;
 Table	Create Table
 t1	CREATE TABLE "t1" (
-  "var" varchar(255) CHARACTER SET utf8 DEFAULT NULL,
-  "rec.var" varchar(255) CHARACTER SET utf8 DEFAULT NULL
+  "var" text CHARACTER SET utf8 DEFAULT NULL,
+  "rec.var" text CHARACTER SET utf8 DEFAULT NULL
 )
 DROP TABLE t1;
 DROP PROCEDURE p1;