fix(ui): avoid recursiveness and invalid memory access #28578

Problem:  Calling :redraw from vim.ui_attach() callback results in
          recursive cmdline/message events.
Solution: Avoid recursiveness where possible and replace global "call_buf"
          with separate, temporary buffers for each event so that when a Lua
          callback for one event fires another event, that does not result
          in invalid memory access.

src/nvim/ui_defs.h

@@ -63,7 +63,6 @@ typedef struct {
   PackerBuffer packer;
 
   const char *cur_event;  ///< name of current event (might get multiple arglists)
-  Array call_buf;  ///< buffer for constructing a single arg list (max 16 elements!)
 
   // We start packing the two outermost msgpack arrays before knowing the total
   // number of elements. Thus track the location where array size will need