[PowerDisplay] Debounced + wheel-scrollable brightness/contrast/volume sliders

[niels9001]

Summary of the Pull Request

The brightness / contrast / volume sliders in the PowerDisplay flyout previously committed to hardware (DDC/CI) only on PointerCaptureLost plus arrow-key KeyUp. That doesn't work reliably on touchscreens — tap-on-track issues no pointer capture, and the Slider / Thumb doesn't always bubble PointerCaptureLost on touch — so the value the user dialed in never reached the monitor.

This PR replaces that wiring with the simpler approach we actually wanted: a TwoWay Value binding plus a debounced commit in the view-model. ValueChanged runs the setter on every move, but a 200 ms DispatcherQueueTimer (restarted on each change) collapses the entire interaction into a single DDC/CI write once the user stops sliding. Mouse, touch, tap-on-track, and held arrow keys all use the same code path.

It also adds a small SliderExtensions helper (Toolkit-style attached properties) so the brightness / contrast / volume sliders can be adjusted by mouse-wheel scroll. The wheel event is marked handled so the parent ScrollViewer does not also scroll, and the existing 200 ms debounce coalesces wheel input into a single DDC/CI write.

PR Checklist

• Closes: Power Display Slide Control with Touch Screen Monitor #47724
• Communication: I've discussed this with core contributors already.
• Tests: Manual smoke; no automated coverage exists for the slider flyout.
• Localization: No new end-user-facing strings.
• Dev docs: N/A
• New binaries: N/A
• Documentation updated: N/A

Detailed Description of the Pull Request / Additional comments

Debounced commit

• MonitorViewModel.Brightness/Contrast/Volume setters now: assign field → OnPropertyChanged() → ScheduleCommit(...) which (re)starts a per-metric DispatcherQueueTimer. On Tick the closure calls SetBrightnessAsync(_brightness) (etc.), reading the latest field value so intermediate drag values are coalesced into one hardware write.
• SetBrightnessAsync / SetContrastAsync / SetVolumeAsync (used by hotkeys, profile load, hardware refresh) keep their immediate-apply behavior — they bypass the public setters, so a TwoWay source-update from one of those paths does not reschedule a commit.
• MonitorViewModel.Dispose() stops the three timers. Pending writes are intentionally dropped: Dispose only runs when the monitor is gone (unplug / refresh) or the app is shutting down, in which case a hardware write would race a half-torn-down MonitorManager.
• AppConstants.UI.SliderCommitDebounceMs = 200 is the single source of truth for the delay.
• Removed the six Handle{Brightness|Contrast|Volume}{PointerCaptureLost|KeyUp} methods and the now-unused IsArrowKey helper.
• using DispatcherQueueTimer = Microsoft.UI.Dispatching.DispatcherQueueTimer; alias avoids ambiguity with Windows.System.DispatcherQueueTimer.

Wheel-scrollable sliders

• New PowerDisplay.Helpers.SliderExtensions — a Toolkit-style public static class <Control>Extensions with two attached properties:
  • SliderExtensions.IsMouseWheelEnabled (bool) — opt in to wheel input.
  • SliderExtensions.MouseWheelChange (double, default NaN → falls back to the slider's own Slider.SmallChange) — per-notch delta.
• Handler computes notches = MouseWheelDelta / 120, clamps to [Minimum, Maximum], sets Value, and marks e.Handled = true so the enclosing MainScrollViewer doesn't also scroll.
• Wired on the brightness, contrast, and volume sliders with MouseWheelChange="5" (20 notches for a full sweep).
• Body has zero PowerDisplay-specific dependencies (only Microsoft.UI.Xaml.*) so the helper is straightforward to lift into the WinUI Community Toolkit later.

Validation Steps Performed

• tools/build/build.cmd against src/modules/powerdisplay/PowerDisplay/PowerDisplay.csproj — exit code 0.
• Manual smoke on a touchscreen device:
  • Touch drag thumb 50 → 80, lift finger → monitor commits once at 80.
  • Tap on the track at 25 % → monitor commits once at 25 %.
• Manual smoke with mouse:
  • Drag 50 → 80, release → exactly one DDC/CI write at 80.
• Manual smoke with keyboard:
  • Hold Right arrow on the brightness slider → repeated nudges collapse into a single write 200 ms after key release.
• Manual smoke with mouse wheel:
  • Hover brightness slider, scroll wheel → value moves by 5 per notch, monitor commits once after scrolling stops.
  • Wheel over a slider does not scroll the flyout's MainScrollViewer; wheel outside the sliders still scrolls.
  • Wheel past Minimum / Maximum clamps at the boundary.
• Hotkey-driven brightness change still applies immediately (regression check on the SetBrightnessAsync path).
• DisplayChangeWatcher-driven hardware refresh does not schedule a spurious commit.

[Raiwulf]

is it possible to include controls for switching display signals per-monitor? a dropdown to select HDMI1-2/DP1-2 and other inputs from this tool would be very useful. That way we can ignore hardware buttons