refactor(ui): remove some superfluous ui_flush() calls

- <expr> mapping has no business saving and restoring the
  low-level UI cursor. The cursor will be put in a reasonable
  position after input is processed, chill out.
- TUI handles output needed for suspend
- vgetc() family of function does flushing

src/nvim/eval.c

@@ -7469,7 +7469,6 @@ void ex_execute(exarg_T *eap)
     if (eap->cmdidx == CMD_echomsg) {
       msg_ext_set_kind("echomsg");
       msg_attr(ga.ga_data, echo_attr);
-      ui_flush();
     } else if (eap->cmdidx == CMD_echoerr) {
       // We don't want to abort following commands, restore did_emsg.
       int save_did_emsg = did_emsg;

src/nvim/eval/userfunc.c

@@ -2150,8 +2150,7 @@ void ex_function(exarg_T *eap)
             }
           }
           msg_prt_line(FUNCLINE(fp, j), false);
-          ui_flush();                  // show a line at a time
-          os_breakcheck();
+          line_breakcheck();  // show multiple lines at a time!
         }
         if (!got_int) {
           msg_putchar('\n');

src/nvim/ex_cmds.c

@@ -1507,7 +1507,6 @@ void print_line(linenr_T lnum, int use_number, int list)
   print_line_no_prefix(lnum, use_number, list);
   if (save_silent) {
     msg_putchar('\n');
-    ui_flush();
     silent_mode = save_silent;
   }
   info_message = false;

src/nvim/ex_docmd.c

@@ -4838,13 +4838,9 @@ static void ex_stop(exarg_T *eap)
   }
   apply_autocmds(EVENT_VIMSUSPEND, NULL, NULL, false, NULL);
 
-  // TODO(bfredl): the TUI should do this on suspend
-  ui_cursor_goto(Rows - 1, 0);
-  ui_call_grid_scroll(1, 0, Rows, 0, Columns, 1, 0);
+  ui_call_suspend();
   ui_flush();
-  ui_call_suspend();  // call machine specific function
 
-  ui_flush();
   maketitle();
   resettitle();  // force updating the title
   ui_refresh();  // may have resized window

src/nvim/getchar.c

@@ -2218,9 +2218,6 @@ static int handle_mapping(int *keylenp, const bool *timedout, int *mapdepth)
     if (mp->m_expr) {
       const int save_vgetc_busy = vgetc_busy;
       const bool save_may_garbage_collect = may_garbage_collect;
-      const int save_cursor_row = ui_current_row();
-      const int save_cursor_col = ui_current_col();
-      const handle_T save_cursor_grid = ui_cursor_grid();
       const int prev_did_emsg = did_emsg;
 
       vgetc_busy = 0;
@@ -2232,14 +2229,10 @@ static int handle_mapping(int *keylenp, const bool *timedout, int *mapdepth)
       }
       map_str = eval_map_expr(mp, NUL);
 
-      // The mapping may do anything, but we expect it to take care of
-      // redrawing.  Do put the cursor back where it was.
-      ui_grid_cursor_goto(save_cursor_grid, save_cursor_row, save_cursor_col);
-      ui_flush();
-
+      if ((map_str == NULL || *map_str == NUL)) {
         // If an error was displayed and the expression returns an empty
         // string, generate a <Nop> to allow for a redraw.
-      if (prev_did_emsg != did_emsg && (map_str == NULL || *map_str == NUL)) {
+        if (prev_did_emsg != did_emsg) {
           char buf[4];
           xfree(map_str);
           buf[0] = (char)K_SPECIAL;
@@ -2255,6 +2248,10 @@ static int handle_mapping(int *keylenp, const bool *timedout, int *mapdepth)
             }
             redrawcmd();
           }
+        } else if (State & (MODE_NORMAL | MODE_INSERT)) {
+          // otherwise, just put back the cursor
+          setcursor();
+        }
       }
 
       vgetc_busy = save_vgetc_busy;

src/nvim/option.c

@@ -1549,7 +1549,6 @@ int do_set(char *arg, int opt_flags)
     silent_mode = false;
     info_message = true;        // use os_msg(), not os_errmsg()
     msg_putchar('\n');
-    ui_flush();
     silent_mode = true;
     info_message = false;       // use os_msg(), not os_errmsg()
   }

src/nvim/popupmenu.c

@@ -1092,7 +1092,6 @@ void pum_show_popupmenu(vimmenu_T *menu)
     pum_is_drawn = true;
     pum_redraw();
     setcursor_mayforce(true);
-    ui_flush();
 
     int c = vgetc();
 

src/nvim/ui.c

@@ -472,11 +472,6 @@ int ui_current_col(void)
   return cursor_col;
 }
 
-handle_T ui_cursor_grid(void)
-{
-  return cursor_grid_handle;
-}
-
 void ui_flush(void)
 {
   assert(!ui_client_channel_id);