vim-patch:8.1.0822: peeking and flushing output slows down execution (#25629)

Problem:    Peeking and flushing output slows down execution.
Solution:   Do not update the mode message when global_busy is set.  Do not
            flush when only peeking for a character. (Ken Takata)

cb574f4154

src/nvim/drawline.c

@@ -3287,5 +3287,5 @@ static void win_put_linebuf(win_T *wp, int row, int coloff, int endcol, int clea
   }
 
   grid_adjust(&grid, &row, &coloff);
-  grid_put_linebuf(grid, row, coloff, 0, endcol, clear_width, wp->w_p_rl, bg_attr, wrap, false);
+  grid_put_linebuf(grid, row, coloff, 0, endcol, clear_width, wp->w_p_rl, bg_attr, wrap);
 }

src/nvim/getchar.c

@@ -2861,8 +2861,10 @@ int inchar(uint8_t *buf, int maxlen, long wait_time)
     }
 
     // Always flush the output characters when getting input characters
-    // from the user.
-    ui_flush();
+    // from the user and not just peeking.
+    if (wait_time == -1L || wait_time > 10L) {
+      ui_flush();
+    }
 
     // Fill up to a third of the buffer, because each character may be
     // tripled below.

src/nvim/grid.c

@@ -481,11 +481,8 @@ void grid_line_flush(void)
     return;
   }
 
-  int row = grid_line_row;
-
-  bool invalid_row = grid != &default_grid && grid_invalid_row(grid, row) && grid_line_first == 0;
-  grid_put_linebuf(grid, row, grid_line_coloff, grid_line_first, grid_line_last, grid_line_last,
-                   false, 0, false, invalid_row);
+  grid_put_linebuf(grid, grid_line_row, grid_line_coloff, grid_line_first, grid_line_last,
+                   grid_line_last, false, 0, false);
 }
 
 /// flush grid line but only if on a valid row
@@ -620,7 +617,7 @@ static int grid_char_needs_redraw(ScreenGrid *grid, int col, size_t off_to, int
 /// If "wrap" is true, then hint to the UI that "row" contains a line
 /// which has wrapped into the next row.
 void grid_put_linebuf(ScreenGrid *grid, int row, int coloff, int col, int endcol, int clear_width,
-                      bool rl, int bg_attr, bool wrap, bool invalid_row)
+                      bool rl, int bg_attr, bool wrap)
 {
   bool redraw_next;                         // redraw_this for next character
   bool clear_next = false;
@@ -639,6 +636,7 @@ void grid_put_linebuf(ScreenGrid *grid, int row, int coloff, int col, int endcol
     return;
   }
 
+  bool invalid_row = grid != &default_grid && grid_invalid_row(grid, row) && col == 0;
   size_t off_to = grid->line_offset[row] + (size_t)coloff;
   const size_t max_off_to = grid->line_offset[row] + (size_t)grid->cols;