GPII-4011: Showing the volume change on the screen

[stegru]

This sets the volume to almost the required value, then uses the shell to perform the final increment causing the volume to show on screen.

The diff shown for VolumeControl.cpp is exaggerated, so here's a picture of the real changes:

[gpii-bot]

CI job passed: https://ci.gpii.net/job/windows-tests/998/

[amb26]

This pull needs some dedicated unit tests for the newly added nativeSettingsHandler code

[gpii-bot]

CI job passed: https://ci.gpii.net/job/windows-tests/1249/

[javihernandez]

@stegru, I see that @amb26 asked for a unit test for this functionality. Can you provide it before getting Chris to review it?

[stegru]

I'm going to leave this one as-is, and move the volume control in-process later: GPII-4445.