patch 8.2.1752: GTK GUI: cannot map alt-? with <A-?>

Problem:    GTK GUI: cannot map alt-? with <A-?>. (Ingo Karkat)
Solution:   Adjust the characters for which the shift modifier is removed.
            (closes #7016)  Make Motif and Win32 use the same function as GTK.
diff --git a/src/gui_w32.c b/src/gui_w32.c
index 19db1a3..5bc5a39 100644
--- a/src/gui_w32.c
+++ b/src/gui_w32.c
@@ -842,8 +842,7 @@
     ch = simplify_key(ch, &modifiers);
     // remove the SHIFT modifier for keys where it's already included, e.g.,
     // '(' and '*'
-    if (ch < 0x100 && !isalpha(ch) && isprint(ch))
-	modifiers &= ~MOD_MASK_SHIFT;
+    modifiers = may_remove_shift_modifier(modifiers, ch);
 
     // Unify modifiers somewhat.  No longer use ALT to set the 8th bit.
     ch = extract_modifiers(ch, &modifiers, FALSE, NULL);