Fix wrong brightnessOverriddenByWindow state in BrightnessSlider

In case brightnessOverriddenByWindow state may lost when switching apps
then scrolling down QuickSettingsPanel to trigger BrightnessSlider
recomposition.

Use State.value directly to ensure getting up-to-date state.

Flag: com.android.systemui.check_lockscreen_gone_transition
Flag: com.android.systemui.qs_ui_refactor_compose_fragment
Bug: 363225340
Test: manual
  1) enable com.android.systemui.qs_ui_refactor_compose_fragment flag
  2) launch NetFlix app
  3) scroll down the QuickSettingsPanel
  4) Swipe the brightness slider
  5) verify BrightnessWarningToast will show up expectedly
Test: atest -d PlatformScenarioTests:SwipeBrightnessShowToast when
  enabling com.android.systemui.qs_ui_refactor_compose_fragment flag
Change-Id: I2610e652f2f216c20d52db8ef9ae80ba11974d13