Eye Gaze and Button FocusTimeout

[davilovick]

Overview

This PR introduce two changes:

• GazeProvider has been changed to allow the possibility to use the Eye Gaze. This feature is only supported in HoloLens 2 device.
• PressableButton has the property FocusSelectionTime. If a button is focused during the time specified in the property, the button will be pressed. Additionally, this PR modify the IPressableButtonFeedback class adding the void FocusTimeout(float timeout), allowing components to represent visually the timeout process till the button will be pressed.

How to test

1. Create a MRTK application.
2. In the XRScene, set the property EnableEyeGaze to true, this will enable the eye gaze.
3. With your eye gaze (in Hololens) or with a controller, focus one of the three round buttons during 2 seconds. The button must be pressed.

[MarcosCobena]

Hi @davilovick,

I have successfully added eye tracking feature to our project (see feature/tecnatom-guiadohololens branch) by enabling it on two of our buttons.

Please consider adding this commit to the PR in case you find it suitable:

247ce73

Thank you for all the hard work mate,

—Marcos