Fixes the button holding test randomly failing on Mac

[raffaeler]

This PR aim to fix the holding button test which randomly fails on Mac.
Since the holding state is measured with a System.Threading.Timer, it probably failed because the Timer thread was not scheduled before the assert made on the main (test) thread.

This change does the following:

• Parameterize the TestButton to use shorter debounce and holding times
• Measure the actual time elapsed when the holding event happens (if ever)

Microsoft Reviewers: Open in CodeFlow

[raffaeler]

FWIW Here is the failure log before these changes:

The core error was an assert failure on the boolean holding state:

[xUnit.net 00:00:05.76]     Iot.Device.Button.Tests.ButtonTests.If_Button_Is_Held_Holding_Event_Fires [FAIL]
  Failed Iot.Device.Button.Tests.ButtonTests.If_Button_Is_Held_Holding_Event_Fires [2 s]
  Error Message:
   holding
Expected: True
Actual:   False
  Stack Trace:
     at Iot.Device.Button.Tests.ButtonTests.If_Button_Is_Held_Holding_Event_Fires() in /Users/runner/work/1/s/src/devices/Button/tests/ButtonTests.cs:line 81

[Ellerbach]

Looks good! Thanks for fixing it!

[raffaeler]

There may be other tests having the same issue.
But IMHO is better to see how this goes and then I'll proceed with the others.