Defining shortcuts for both Num+, and Num+. gives an ambiguous shortcut warning (and fails to work) when using the German keyboard layout (Windows only)

This is similar to QTBUG-57938 but rather less important; a given keyboard will only have either a Num+. key or a Num+, key, so it's not useful to define both shortcuts. Nonetheless this was reported by a user of our application (we had inadvertently left the English shortcut defined in the German version).

STEPS TO REPRODUCE
1. Build and run the attached application on Windows.
2. Connect a German keyboard and switch to the German keyboard layout in the OS.
3. Observe that there are two menu entries, one with shortcut 'Num+.' and one with shortcut 'Num+,'.
4. Ensure the Application Output is visible in Qt Creator.
5. Press the ',' key on the numeric keypad.

EXPECTED: The shortcut for Num+, is triggered.
ACTUAL: An ambiguous shortcut for Num+. is reported in the app output.

I tried to work out what was going on here; it seems as though the 'fallback' case in QWindowsKeyMapper is mapping the virtual code for this key (0x6E, VK_DECIMAL) to Qt::Key_Period, even though the keyboard layout correctly returns a comma. I couldn't really work out why this fallback was necessary.