Fix: Allow Key Bindings with Shift-Modified Keys

This commit allows to set key bindings that contain
a key modified by a Shift key (e.g. `Ctrl + {`).
For example, after pressing `Ctrl + Shift + [`,
a key binding will be set to `Ctrl + {` as opposed
to `Ctrl + Shift + {` as before.

This is achieved by checking whether a key changes its
value when a Shift key is down. If it does, then the
Shift modifier is removed from `mods`. One exception:
if a key binding contains a letter then the Shift
modifier is not removed. This is because, for some
reason, a key value of a letter is never modified by the
Shift modifier and always corresponds to a key value of
a lowercase character. This is already handled in
`terminatorlib/keybindings.py`.

Resolves: #149

terminatorlib/prefseditor.py

@@ -1550,6 +1550,21 @@ class PrefsEditor:
 
     def on_cellrenderer_accel_edited(self, liststore, path, key, mods, _code):
         """Handle an edited keybinding"""
+        if mods & Gdk.ModifierType.SHIFT_MASK:
+            key_with_shift = Gdk.Keymap.translate_keyboard_state(
+                self.keybindings.keymap,
+                hardware_keycode=_code,
+                state=Gdk.ModifierType.SHIFT_MASK,
+                group=0,
+            )
+            keyval_lower, keyval_upper = Gdk.keyval_convert_case(key)
+
+            # Remove the Shift modifier from `mods` if a new key binding doesn't
+            # contain a letter and its key value (`key`) can't be modified by a
+            # Shift key.
+            if key_with_shift.level != 0 and keyval_lower == keyval_upper:
+                mods = Gdk.ModifierType(mods & ~Gdk.ModifierType.SHIFT_MASK)
+
         celliter = liststore.get_iter_from_string(path)
         liststore.set(celliter, 2, key, 3, mods)