patch 8.2.1772: cannot use CTRL-W <Down> to move out of a terminal window

Problem:    Cannot use CTRL-W <Down> to move out of a terminal window.
Solution:   Use special_to_buf() instead of mb_char2bytes(). (closes #7045)

src/terminal.c

@@ -2640,12 +2640,13 @@ if (raw_c > 0)
 	    }
 	    else if (termwinkey == 0 || c != termwinkey)
 	    {
-		char_u buf[MB_MAXBYTES + 2];
+		// space for CTRL-W, modifier, multi-byte char and NUL
+		char_u buf[1 + 3 + MB_MAXBYTES + 1];
 
 		// Put the command into the typeahead buffer, when using the
 		// stuff buffer KeyStuffed is set and 'langmap' won't be used.
 		buf[0] = Ctrl_W;
-		buf[(*mb_char2bytes)(c, buf + 1) + 1] = NUL;
+		buf[special_to_buf(c, mod_mask, FALSE, buf + 1) + 1] = NUL;
 		ins_typebuf(buf, REMAP_NONE, 0, TRUE, FALSE);
 		ret = OK;
 		goto theend;

src/testdir/test_terminal.vim

@@ -1379,6 +1379,23 @@ func Test_terminal_statusline()
   set statusline=
 endfunc
 
+func Test_terminal_window_focus()
+  let winid1 = win_getid()
+  terminal
+  let winid2 = win_getid()
+  call feedkeys("\<C-W>j", 'xt')
+  call assert_equal(winid1, win_getid())
+  call feedkeys("\<C-W>k", 'xt')
+  call assert_equal(winid2, win_getid())
+  " can use a cursor key here
+  call feedkeys("\<C-W>\<Down>", 'xt')
+  call assert_equal(winid1, win_getid())
+  call feedkeys("\<C-W>\<Up>", 'xt')
+  call assert_equal(winid2, win_getid())
+
+  bwipe!
+endfunc
+
 func Api_drop_common(options)
   call assert_equal(1, winnr('$'))
 

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1772,
 /**/
     1771,
 /**/