[NUI] Add SetHiddenInput, GetHiddenInput to TextField

[NUI] Add SetHiddenInput, GetHiddenInput to TextField

Add a HiddenInput struct to pass data of DALi HiddenInputSettings PropertyMap.
The HiddenInput struct can be used as an argument to
SetHiddenInput and GetHiddenInput methods.

// example
var hiddenInput = new Tizen.NUI.Text.HiddenInput();
hiddenInput.Mode = HiddenInputModeType.ShowLastCharacter;
hiddenInput.SubstituteCharacter = '★';
hiddenInput.SubstituteCount = 0;
hiddenInput.ShowLastCharacterDuration = 1000;

field.SetHiddenInput(hiddenInput);

Signed-off-by: Bowon Ryu <bowon.ryu@samsung.com>