QCocoaKeyMapper - correctly update key layouts

QCocoaKeyMapper has 2 bugs:
- fails to update layouts even if input source changed
- while looking for the possible keys it clears bits for
  neededMods thus making later shortcut match impossible

Change-Id: Ie230b973acd5ca6f50b97ca4901ede61b581d273
Task-number: QTBUG-50865
Reviewed-by: Andy Shaw <andy.shaw@theqtcompany.com>
Reviewed-by: Morten Johan Sørvig <morten.sorvig@theqtcompany.com>
Reviewed-by: Timur Pocheptsov <timur.pocheptsov@theqtcompany.com>

src/plugins/platforms/cocoa/qcocoakeymapper.mm

@@ -390,6 +390,11 @@ bool QCocoaKeyMapper::updateKeyboard()
         keyboardInputLocale = QLocale::c();
         keyboardInputDirection = Qt::LeftToRight;
     }
+
+    const auto newMode = keyboard_mode;
+    deleteLayouts();
+    keyboard_mode = newMode;
+
     return true;
 }
 
@@ -412,10 +417,8 @@ void QCocoaKeyMapper::clearMappings()
 
 void QCocoaKeyMapper::updateKeyMap(unsigned short macVirtualKey, QChar unicodeKey)
 {
-    if (updateKeyboard()) {
-        // ### Qt 4 did this:
-        // QKeyMapper::changeKeyboard();
-    }
+    updateKeyboard();
+
     if (keyLayout[macVirtualKey])
         return;
 
@@ -471,9 +474,8 @@ QList<int> QCocoaKeyMapper::possibleKeys(const QKeyEvent *event) const
     for (int i = 1; i < 8; ++i) {
         Qt::KeyboardModifiers neededMods = ModsTbl[i];
         int key = kbItem->qtKey[i];
-        if (key && key != baseKey && ((keyMods & neededMods) == neededMods)) {
-            ret << int(key + (keyMods & ~neededMods));
-        }
+        if (key && key != baseKey && ((keyMods & neededMods) == neededMods))
+            ret << int(key + neededMods);
     }
     return ret;
 }