Prevent proguard from pruning ClockSetting

ClockSetting is populated via gson (using reflection), so proguard
will clean it. This causes gson to silently fail and return and
empty object in some configurations. Annotating the class with
@Keep prevents this from occuring.

Bug: 229771520
Test: Manually tested on userdebug variant
Change-Id: I9a7c3e4c4d66d1c13d58cba5994d5578034a9bf8

packages/SystemUI/shared/src/com/android/systemui/shared/clocks/ClockRegistry.kt

@@ -22,6 +22,7 @@ import android.os.UserHandle
 import android.provider.Settings
 import android.util.Log
 import com.android.systemui.dagger.qualifiers.Main
+import com.android.internal.annotations.Keep
 import com.android.systemui.plugins.ClockController
 import com.android.systemui.plugins.ClockId
 import com.android.systemui.plugins.ClockMetadata
@@ -201,6 +202,7 @@ open class ClockRegistry(
         val provider: ClockProvider
     )
 
+    @Keep
     private data class ClockSetting(
         val clockId: ClockId,
         val _applied_timestamp: Long?