Split Column_definition::create_length_to_internal_length() to virtual methods in Type_handler

This code is not friendly to pluggable data types:

void Column_definition::create_length_to_internal_length(void)

{

  switch (real_field_type()) {

  case MYSQL_TYPE_TINY_BLOB:

  ...

  }

}

As of MDEV creation time, the only place where create_length_to_internal_length() is used (see bb-10.2-ext and 10.3 branches) is a loop inside mysql_prepare_create_table():

/* Check if we have used the same field name before */

for (dup_no=0; (dup_field=it2++) != sql_field; dup_no++)

{

...

    if (!(sql_field->flags & NOT_NULL_FLAG))

      null_fields--;

    sql_field->flags=             dup_field->flags;

    sql_field->create_length_to_internal_length();

    sql_field->interval=          dup_field->interval;

    sql_field->vcol_info=         dup_field->vcol_info;

...

}

This code is responsible for queries like this:

CREATE TABLE t2 (a INT) AS SELECT a FROM t1;

I.e. t1.a is queried, but its data type is redefined.

Under terms of this task we'll do the following:

• Introduce a new virtual method in Type_handler:

  virtual bool Column_definition_redefine_stage1(Column_definition *def,

  const Column_definition *dup,

  const handler *file,

  const Schema_specification_st *)

  const;

• Move the entire redefinition code (responsible for copying members from dup_field to sql_field):
• Data type independent code will go into a shared method Column_definition::redefine_stage1_common()
• Data type specific code will go to relevant virtual implementations of Column_definition_redefine_stage1. Every implementation will include a call for redefine_stage1_common() followed by data specific code. For example, the method responsible for handling DECIMAL, will look like:

  bool Type_handler_newdecimal::

  Column_definition_redefine_stage1(Column_definition *def,

  const Column_definition *dup,

  const handler *file,

  const Schema_specification_st *schema)

  const

  {

  def->redefine_stage1_common(dup, file, schema);

  def->create_length_to_internal_length_newdecimal();

  return false;

  }

• Remove Column_definition::create_length_to_internal_length()