Sys - Support for windows

[adrian-moisa]

• changed translation country code (zh_HK -> zh_hk) to lower case, which is required for i18n_extension used in flutter_quill.
• add localization in example's main to demonstrate translation. (this is not a necessary change)
• issue https://github.com/singerdmx/flutter-quill/issues/861: add selection's copy / paste toolbar, escape to hide toolbar, mouse right click to show toolbar, ctrl-Y / ctrl-Z to undo / redo
• Image and video displayed in Windows platform caused screen flickering while selecting text, a sample_data_nomedia.json asset is added for Desktop to demonstrate the added features. (this is not a necessary change)
• Known issue: keyboard action sometimes causes exception mentioned in Flutter's issue #106475 (https://github.com/flutter/flutter/issues/106475)
• Known issue: user needs to click the editor to get focus before toolbar is able to display.
• Ref: 946, 861

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