The intent of this patch is to avoid copying arguments from
a pair "Item **args, uint arg_count" to List<Item> in
sp_head::execute_function(). If the number of a stored function parameters
is huge, such copying can affect performance.

Change:
1. Adding a new method Row_definition_list::adjust_formal_params_to_actual_params,
   which accepts a pair of "Item **, uint".
2. Modifying the code to use the new method:
   - the calls for sp_rcontext::retrieve_field_definitions() and
     Row_definition_list::adjust_formal_params_to_actual_params() have
     been moved from sp_rcontext::create() to sp_head::rcontext_create(),
     to handle different argument notations easier (Item** vs List<Item>).
   - sp_rcontext::create() now assumes that the passed Row_definition_list
     is already adjusted to the actual SP parameters, and all "TYPE OF"
     and "ROWTYPE OF" references are resolved.
3. Removing creation of List<Item> in sp_head::execute_procedure(),
   using the code with "Item**, uint" notation instead.
4. Improvement of the code for MDEV-10577:
   As a good side effect, this patch gets rid of double security context
   switch inside sp_head::execute_trigger():
   sp_rcontext is created when the context is already switched,
   so the second context switch inside sp_head::rcontext_create() was
   redundant. This is solved by adding a "bool switch_secutiry_ctx" parameter
   to rcontext_create(), so now execute_function() and execute_procedure()
   pass "true", while execute_trigger() passes "false".