fix(ui): ext_cmdline should not move cursor to curwin

Problem:  The ext_cmdline cursor position on the screen seems to rely on
          an implicit assumption that the event listener implements a
          cmdline window that is made the current window which is
          problematic (e.g. breaks 'incsearch' in the actual current
          window).
Solution: Remove this assumption and allow nvim_win_set_cursor() to move
          the cursor on the screen to a non-current window (previous
          commit).

src/nvim/ex_getln.c

@@ -767,7 +767,7 @@ static uint8_t *command_line_enter(int firstc, int count, int indent, bool clear
   }
 
   setmouse();
-  ui_cursor_shape();               // may show different cursor shape
+  setcursor();
 
   TryState tstate;
   Error err = ERROR_INIT;
@@ -927,7 +927,6 @@ static uint8_t *command_line_enter(int firstc, int count, int indent, bool clear
   }
   may_trigger_modechanged();
   setmouse();
-  ui_cursor_shape();            // may show different cursor shape
   sb_text_end_cmdline();
 
 theend:
@@ -3859,7 +3858,6 @@ void cursorcmd(void)
     if (ccline.redraw_state < kCmdRedrawPos) {
       ccline.redraw_state = kCmdRedrawPos;
     }
-    setcursor();
     return;
   }
 
@@ -4553,6 +4551,7 @@ static int open_cmdwin(void)
   State = save_State;
   may_trigger_modechanged();
   setmouse();
+  setcursor();
 
   return cmdwin_result;
 }

test/functional/ui/cmdline_spec.lua

@@ -824,6 +824,29 @@ local function test_cmdline(linegrid)
                                |
     ]])
   end)
+
+  it('does not move cursor to curwin #20309', function()
+    local win = api.nvim_get_current_win()
+    command('norm icmdlinewin')
+    command('new')
+    command('norm icurwin')
+    feed(':')
+    api.nvim_win_set_cursor(win, { 1, 7 })
+    screen:expect {
+      grid = [[
+      curwin                   |
+      {3:[No Name] [+]            }|
+      cmdline^win               |
+      {2:[No Name] [+]            }|
+                               |
+    ]],
+      cmdline = { {
+        content = { { '' } },
+        firstc = ':',
+        pos = 0,
+      } },
+    }
+  end)
 end
 
 -- the representation of cmdline and cmdline_block contents changed with ext_linegrid