vim-patch:9.1.2001: cursor may end up in wrong window after :botright copen (#37056)

Problem:  After :botright copen and closing the quikfix window, the
          cursor ends up in the wrong window. The problem is fr_child
          always points to the first (leftmost for FR_ROW, topmost for
          FR_COL) child frame. When do :vsplit, the new window is
          created on the left, and frame_insert() updates the parent's
          fr_child to point to this new left window.
Solution: Create a snapshot before open the quickfix window and restore
          it when close it (glepnir).

closes: vim/vim#18961

b43f9ded7e

Co-authored-by: glepnir <glephunter@gmail.com>

test/old/testdir/test_quickfix.vim

@@ -6980,4 +6980,15 @@ func Test_vimgrep_dummy_buffer_keep()
   %bw!
 endfunc
 
+func Test_quickfix_restore_current_win()
+  let curwin = win_getid()
+  vsplit Xb
+  wincmd p
+  botright copen
+  cclose
+
+  call assert_equal(curwin, win_getid())
+  bw! Xb
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab