MDEV-16584 SP with a cursor inside a loop wastes THD memory aggressively

Problem:

push_handler() created sp_handler_entry instances on THD::main_mem_root,
which is freed only after the SP instructions execution.
So in case of a CONTINUE HANDLER inside a loop (e.g. WHILE) this approach
leaked thread memory on every loop iteration.

Changes:
- Removing sp_handler_entry declaration, it's not really needed.
- Fixing the data type of sp_rcontext::m_handlers from
  Dynamic_array<sp_handler_entry*> to Dynamic_array<sp_instr_hpush_jump*>
- Fixing sp_rcontext::push_handler() to push the pointer to
  an sp_instr_hpush_jump instance to the handler stack.
  This instance contains everything we need.
  There is no a need to allocate anything else.

1 files changed, 0 insertions, 2 deletions

diff --git a/sql/sp_head.h b/sql/sp_head.h
index 580859b8831..cf934603cf0 100644
--- a/sql/sp_head.h
+++ b/sql/sp_head.h
@@ -1677,8 +1677,6 @@ public:
   { return m_handler; }
 
 private:
-
-private:
   /// Handler.
   sp_handler *m_handler;