perf(messages): don't call ui_flush() per message line in various places

When msgsep is used, message scrolling is emulated. To make message
output fast, inhibit emulated scrolling until the full message text
is known

src/nvim/cmdexpand.c

@@ -717,7 +717,6 @@ int showmatches(expand_T *xp, int wildmenu)
         msg_clr_eos();
         msg_putchar('\n');
       }
-      ui_flush();                          // show one line at a time
       if (got_int) {
         got_int = false;
         break;

src/nvim/cmdhist.c

@@ -650,7 +650,6 @@ void ex_history(exarg_T *eap)
             STRCAT(IObuff, hist[i].hisstr);
           }
           msg_outtrans((char *)IObuff);
-          ui_flush();
         }
         if (i == idx) {
           break;

src/nvim/ex_cmds.c

@@ -5004,7 +5004,6 @@ void ex_oldfiles(exarg_T *eap)
         msg_outtrans((char *)tv_get_string(TV_LIST_ITEM_TV(li)));
         msg_clr_eos();
         msg_putchar('\n');
-        ui_flush();                  // output one line at a time
         os_breakcheck();
       }
     });

src/nvim/ex_docmd.c

@@ -4833,7 +4833,6 @@ static void ex_print(exarg_T *eap)
       if (++eap->line1 > eap->line2) {
         break;
       }
-      ui_flush();                  // show one line at a time
     }
     setpcmark();
     // put cursor at last line
@@ -5035,7 +5034,6 @@ static void ex_tabs(exarg_T *eap)
     msg_putchar('\n');
     vim_snprintf((char *)IObuff, IOSIZE, _("Tab page %d"), tabcount++);
     msg_outtrans_attr((char *)IObuff, HL_ATTR(HLF_T));
-    ui_flush();            // output one line at a time
     os_breakcheck();
 
     FOR_ALL_WINDOWS_IN_TAB(wp, tp) {
@@ -5054,7 +5052,6 @@ static void ex_tabs(exarg_T *eap)
         home_replace(wp->w_buffer, wp->w_buffer->b_fname, (char *)IObuff, IOSIZE, true);
       }
       msg_outtrans((char *)IObuff);
-      ui_flush();                  // output one line at a time
       os_breakcheck();
     }
   }

src/nvim/mapping.c

@@ -214,7 +214,6 @@ static void showmap(mapblock_T *mp, bool local)
     last_set_msg(mp->m_script_ctx);
   }
   msg_clr_eos();
-  ui_flush();                          // show one line at a time
 }
 
 /// Replace termcodes in the given LHS and RHS and store the results into the

src/nvim/mark.c

@@ -925,7 +925,6 @@ static void show_one_mark(int c, char_u *arg, pos_T *p, char_u *name_arg, int cu
           msg_outtrans_attr((char *)name, current ? HL_ATTR(HLF_D) : 0);
         }
       }
-      ui_flush();  // show one line at a time
     }
     if (mustfree) {
       xfree(name);
@@ -1058,7 +1057,6 @@ void ex_jumps(exarg_T *eap)
       xfree(name);
       os_breakcheck();
     }
-    ui_flush();
   }
   if (curwin->w_jumplistidx == curwin->w_jumplistlen) {
     msg_puts("\n>");
@@ -1101,7 +1099,6 @@ void ex_changes(exarg_T *eap)
       xfree(name);
       os_breakcheck();
     }
-    ui_flush();
   }
   if (curwin->w_changelistidx == curbuf->b_changelistlen) {
     msg_puts("\n>");

src/nvim/ops.c

@@ -3866,7 +3866,6 @@ void ex_display(exarg_T *eap)
         if (n > 1 && yb->y_type == kMTLineWise) {
           msg_puts_attr("^J", attr);
         }
-        ui_flush();  // show one line at a time
       }
       os_breakcheck();
     }

src/nvim/option.c

@@ -3355,7 +3355,6 @@ static void showoptions(int all, int opt_flags)
         showoneopt(items[i], opt_flags);
         col += INC;
       }
-      ui_flush();
       os_breakcheck();
     }
   }

src/nvim/quickfix.c

@@ -3094,8 +3094,6 @@ static void qf_list_entry(qfline_T *qfp, int qf_idx, bool cursel)
   if (tbuf != IObuff) {
     xfree(tbuf);
   }
-
-  ui_flush();  // show one line at a time
 }
 
 // ":clist": list all errors

src/nvim/search.c

@@ -3714,7 +3714,6 @@ void find_pattern_in_path(char_u *ptr, Direction dir, size_t len, bool whole, bo
             }
           }
         }
-        ui_flush();                // output each line directly
       }
 
       if (new_fname != NULL) {
@@ -4147,7 +4146,6 @@ static void show_pat_in_path(char_u *line, int type, bool did_show, int action,
       msg_puts(" ");
     }
     msg_prt_line((char *)line, false);
-    ui_flush();                        // show one line at a time
 
     // Definition continues until line that doesn't end with '\'
     if (got_int || type != FIND_DEFINE || p < line || *p != '\\') {

src/nvim/tag.c

@@ -1056,7 +1056,6 @@ void do_tags(exarg_T *eap)
                         ? HL_ATTR(HLF_D) : 0);
       xfree(name);
     }
-    ui_flush();                    // show one line at a time
   }
   if (tagstackidx == tagstacklen) {     // idx at top of stack
     msg_puts("\n>");