vim-patch:8.2.4018: ml_get error when win_execute redraws with Visual selection

Problem:    ml_get error when win_execute redraws with Visual selection.
Solution:   Disable Visual area temporarily. (closes vim/vim#9479)
18f4740f04

{switch_to/restore}_win_for_buf is N/A (marked as such in v8.0.0860; currently
only used in Vim's if_py).

Add a modeline to test_execute_func.vim.

src/nvim/window.h

@@ -32,6 +32,14 @@
 #define MIN_COLUMNS     12      // minimal columns for screen
 #define MIN_LINES       2       // minimal lines for screen
 
+/// Structure used by switch_win() to pass values to restore_win()
+typedef struct {
+  win_T *sw_curwin;
+  tabpage_T *sw_curtab;
+  bool sw_same_win;  ///< VIsual_active was not reset
+  bool sw_visual_active;
+} switchwin_T;
+
 #ifdef INCLUDE_GENERATED_DECLARATIONS
 # include "window.h.generated.h"
 #endif