patch 8.2.4844: <C-S-I> is simplified to <S-Tab>

Problem:    <C-S-I> is simplified to <S-Tab>.
Solution:   Do not simplify CTRL if there is also SHIFT. (closes #10313)

src/getchar.c

@@ -1634,7 +1634,7 @@ merge_modifyOtherKeys(int c_arg, int *modifiers)
 {
     int c = c_arg;
 
-    if (*modifiers & MOD_MASK_CTRL)
+    if ((*modifiers & MOD_MASK_CTRL) && !(*modifiers & MOD_MASK_SHIFT))
     {
 	if ((c >= '`' && c <= 0x7f) || (c >= '@' && c <= '_'))
 	{

src/testdir/test_gui.vim

@@ -1560,4 +1560,10 @@ func Test_gui_findrepl()
   bw!
 endfunc
 
+func Test_gui_CTRL_V()
+  call feedkeys(":let g:str = '\<C-V>\<*C-S-I>\<C-V>\<*C-S-@>'\<CR>", 'tx')
+  call assert_equal('<C-S-I><C-S-@>', g:str)
+  unlet g:str
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab

src/version.c

@@ -746,6 +746,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    4844,
 /**/
     4843,
 /**/