Add class Function_collection

Data type plugins should be able to provide their own sets of built-in functions.

Let's add a new class Function_collection, as follows:

class Function_collection

{

public:

  virtual ~Function_collection() {}

  virtual bool init()= 0;

  virtual void cleanup()= 0;

  virtual Create_func *find_native_function_builder(THD *thd,

                                                    const LEX_CSTRING &name)

                                                    const= 0;

};

and, as a prove of the conceipt, move all GIS functions into a new class Function_collection_geometry.

• The method init() will do the collection initialization, e.g. create a hash to lookup Create_func builders by function names.
• The method cleanup will free all memory allocated by init(), e.g. free the lookup hash.
• The method find_native_function_builder will lookup a function by name and return its Create_func builder (or NULL if the function is not found).

This task will also do the following:

• Move all GIS function Create_func_xxx classes from item_create_cc to item_geofunc.cc
• Move definitions of Create_func_arg0, Create_func_arg1, Create_func_arg2, Create_func_arg3 from item_create.cc to item_create.h, so function collection plugins can reuse these classes.
• Remove this code from the bison grammar:

  - | geometry_function

  - {

  -#ifdef HAVE_SPATIAL

  - $$= $1;

  - /* $1 may be NULL, GEOM_NEW not tested for out of memory */

  - if (unlikely($$ == NULL))

  - MYSQL_YYABORT;

  -#else

  - my_yyabort_error((ER_FEATURE_DISABLED, MYF(0), sym_group_geom.name,

  - sym_group_geom.needed_define));

  -#endif

  - }

  - ;

  -

  -geometry_function:

  - CONTAINS_SYM '(' expr ',' expr ')'

  - {

  - $$= GEOM_NEW(thd,

  - Item_func_spatial_precise_rel(thd, $3, $5,

  - Item_func::SP_CONTAINS_FUNC));

  - }

  - | WITHIN '(' expr ',' expr ')'

  - {

  - $$= GEOM_NEW(thd, Item_func_spatial_precise_rel(thd, $3, $5,

  - Item_func::SP_WITHIN_FUNC));

  - }

  and add something like this into the function_call_generic rule:

  | CONTAINS_SYM '(' opt_expr_list ')'

  {

  if (!($$= Lex->make_item_func_call_native_or_parse_error(thd,

  $1, $3)))

  MYSQL_YYABORT;

  }

  | WITHIN '(' opt_expr_list ')'

  {

  if (!($$= Lex->make_item_func_call_native_or_parse_error(thd,

  $1, $3)))

  MYSQL_YYABORT;

  }

• Add a global instance of Function_collection_geometry

Later, in a separate MDEV, we'll add a new plugin type, MYSQL_FUNCTION_COLLECTION_PLUGIN.