MDEV-21073 Collect different grammar rules into a single chunk

On order to unify the two *.yy files easier,
this patch collects all different rules to the end of *.yy files,
so the rule section looks like this:

%%
common rules
different rules

sql/sql_lex.cc

@@ -9741,6 +9741,17 @@ LEX::add_primary_to_query_expression_body(SELECT_LEX_UNIT *unit,
 }
 
 
+SELECT_LEX_UNIT *
+LEX::add_primary_to_query_expression_body(SELECT_LEX_UNIT *unit,
+                                          SELECT_LEX *sel,
+                                          enum sub_select_type unit_type,
+                                          bool distinct)
+{
+  return
+    add_primary_to_query_expression_body(unit, sel, unit_type, distinct,
+                                         thd->variables.sql_mode & MODE_ORACLE);
+}
+
 /**
   Add query primary to a parenthesized query primary
   pruducing a new query expression body
@@ -11130,3 +11141,30 @@ bool LEX::sp_if_after_statements(THD *thd)
   sphead->push_backpatch(thd, i, spcont->push_label(thd, &empty_clex_str, 0));
   return false;
 }
+
+
+sp_condition_value *LEX::stmt_signal_value(const Lex_ident_sys_st &ident)
+{
+  sp_condition_value *cond;
+  /* SIGNAL foo cannot be used outside of stored programs */
+  if (unlikely(spcont == NULL))
+  {
+    my_error(ER_SP_COND_MISMATCH, MYF(0), ident.str);
+    return NULL;
+  }
+  cond= spcont->find_declared_or_predefined_condition(thd, &ident);
+  if (unlikely(cond == NULL))
+  {
+    my_error(ER_SP_COND_MISMATCH, MYF(0), ident.str);
+    return NULL;
+  }
+  bool bad= thd->variables.sql_mode & MODE_ORACLE ?
+            !cond->has_sql_state() :
+            cond->type != sp_condition_value::SQLSTATE;
+  if (unlikely(bad))
+  {
+    my_error(ER_SIGNAL_BAD_CONDITION_TYPE, MYF(0));
+    return NULL;
+  }
+  return cond;
+}

sql/sql_lex.h

@@ -4509,6 +4509,11 @@ struct LEX: public Query_tables_list
                                        bool distinct,
                                        bool oracle);
   SELECT_LEX_UNIT *
+  add_primary_to_query_expression_body(SELECT_LEX_UNIT *unit,
+                                       SELECT_LEX *sel,
+                                       enum sub_select_type unit_type,
+                                       bool distinct);
+  SELECT_LEX_UNIT *
   add_primary_to_query_expression_body_ext_parens(
                                        SELECT_LEX_UNIT *unit,
                                        SELECT_LEX *sel,
@@ -4597,6 +4602,8 @@ struct LEX: public Query_tables_list
   bool stmt_alter_function_start(sp_name *name);
   bool stmt_alter_procedure_start(sp_name *name);
 
+  sp_condition_value *stmt_signal_value(const Lex_ident_sys_st &ident);
+
   Spvar_definition *row_field_name(THD *thd, const Lex_ident_sys_st &name);
 
   bool set_field_type_udt(Lex_field_type_st *type,