Fixed slider value indicator not disappearing after a bit on desktop platform when slider is clicked not dragged (#128137)

In slider.dart within the _startInteraction method and within the below conditional.

"if (!_active && !hasFocus &&
_state.valueIndicatorController.status == AnimationStatus.completed)"

**Changed to:**

"f (!_active &&
_state.valueIndicatorController.status == AnimationStatus.completed)"
This allows the value indicator to disappear after a bit when clicked instead of dragged on Desktop platform. 

I also added a test in slider_test.dart to detect the bug if it ever returns.

Fixes https://github.com/flutter/flutter/issues/123313