Feature flag for which impl. of KeyguardBottomArea

The next CLs introduce a refactor of the internals of
KeyguardBottomAreaView(Controller). This flag is meant to control which
implementation to use in order to limit risk while we work on the
refactor.

Test: Verified, through TheFlippinApp, that the flag exists and that flipping it affects the value read in the SysUI code.
Bug: 235403311
Fixes: 235403311
Change-Id: Ic6c06b047bb5d4b90932dc103a101871f6e4e587

packages/SystemUI/src/com/android/systemui/flags/Flags.java

@@ -81,6 +81,11 @@ public class Flags {
 
     public static final ResourceBooleanFlag FACE_SCANNING_ANIM =
             new ResourceBooleanFlag(205, R.bool.config_enableFaceScanningAnimation);
+    /**
+     * Whether the KeyguardBottomArea(View|Controller) should use the modern architecture or the old
+     * one.
+     */
+    public static final BooleanFlag MODERN_BOTTOM_AREA = new BooleanFlag(206, false);
 
     /***************************************/
     // 300 - power menu