Wrap the code in sp.cc into a class Sp_handler

The code in sp.sp, sp_head.cc, sql_acl.cc, sql_lex.cc, sql_show.cc, sql_yacc*.yy uses a lot of conditions on the routine type, e.g.

  if (type == TYPE_ENUM_FUNCTION)

    do_func;

  else

    do_proc;

Oracle style packages (MDEV-10591) will introduce new SP object types: TYPE_ENUM_PACKAGE_SPEC and TYPE_ENUM_PACKAGE_BODY.
The conditional type-related code will get more complex.

Under terms of this code we'll create a new class Sp_handler with a number of virtual methods, to simplify handling of SP objects of different types and therefore simplify adding packages.

We'll add the be the top level abstract class Sp_handler with this approximate set of virtual methods:

class Sp_handler

{

public:

  virtual const char *show_create_routine_col1_caption() const;

  virtual const char *show_create_routine_col3_caption() const;

  virtual stored_procedure_type type() const;

  virtual LEX_CSTRING type_lex_cstring() const;

  virtual LEX_CSTRING empty_body_lex_cstring() const;

  virtual MDL_key::enum_mdl_namespace get_mdl_type() const;

  virtual sp_cache **get_cache(THD *) const;  

  virtual HASH *priv_hash() const;

  virtual ulong recursion_depth(THD *thd) const;

  virtual void recursion_level_error(THD *thd, const sp_head *sp) const;

};

and will add instantiable sub-classes for certain SP object types:

Sp_handler

  Sp_handler_procedure

  Sp_handler_trigger

  Sp_handler_function

MDEV-10591 will later add Sp_handler_package_spec and Sp_handler_package_body sub-classes.