MDEV-29284 ANALYZE doesn't work with pushed derived tables

There was no actual execution of the SQL of a pushed derived table,
which caused "r_rows" to be always displayed as 0 and "r_total_time_ms"
to show inaccurate numbers.
This commit makes a derived table SQL to be executed by the storage
engine, so the server is able to calculate the number of rows returned
and measure the execution time more accurately

mysql-test/suite/federated/federatedx_create_handlers.result

@@ -190,7 +190,7 @@ FROM federated.t3, (SELECT * FROM federated.t1 WHERE id > 3) t
 WHERE federated.t3.name=t.name;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	r_rows	filtered	r_filtered	Extra
 1	PRIMARY	t3	ALL	NULL	NULL	NULL	NULL	7	7.00	100.00	100.00	
-1	PRIMARY	<derived2>	ref	key0	key0	18	federated.t3.name	2	0.00	100.00	100.00	
+1	PRIMARY	<derived2>	ref	key0	key0	18	federated.t3.name	2	1.00	100.00	100.00	
 2	PUSHED DERIVED	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL
 SELECT *
 FROM federated.t3, (SELECT t1.name FROM federated.t1
@@ -241,7 +241,7 @@ ANALYZE
       "ref": ["federated.t3.name"],
       "r_loops": 7,
       "rows": 2,
-      "r_rows": 0,
+      "r_rows": 0.1429,
       "r_total_time_ms": "REPLACED",
       "filtered": 100,
       "r_filtered": 100,

sql/derived_handler.cc

@@ -40,7 +40,6 @@
 Pushdown_derived::Pushdown_derived(TABLE_LIST *tbl, derived_handler *h)
  : derived(tbl), handler(h)
 {
-  is_analyze= handler->thd->lex->analyze_stmt;
 }
 
 
@@ -57,12 +56,6 @@ int Pushdown_derived::execute()
   if ((err= handler->init_scan()))
     goto error;
 
-  if (is_analyze)
-  {
-    handler->end_scan();
-    DBUG_RETURN(0);
-  }
-
   while (!(err= handler->next_row()))
   {
     if (unlikely(thd->check_killed()))

sql/sql_select.h

@@ -2545,8 +2545,6 @@ class derived_handler;
 
 class Pushdown_derived: public Sql_alloc
 {
-private:
-  bool is_analyze;
 public:
   TABLE_LIST *derived;
   derived_handler *handler;