Add ASSIST_TAP_PASSTHROUGH flag.

Make PhenotypeHelper public.

Bug: 135459244
Test: Manual via adb
Change-Id: I039552bdfde1b0c3ff481af5b4f8813091112391

core/java/com/android/internal/config/sysui/SystemUiDeviceConfigFlags.java

@@ -113,7 +113,7 @@ public final class SystemUiDeviceConfigFlags {
      */
     public static final String PROPERTY_PERMISSIONS_HUB_ENABLED = "permissions_hub_enabled";
 
-    // Flags related to Assistant Handles
+    // Flags related to Assistant
 
     /**
      * (String) Which behavior mode for the Assistant Handles to use.
@@ -190,5 +190,10 @@ public final class SystemUiDeviceConfigFlags {
     public static final String ASSIST_HANDLES_SUPPRESS_ON_APPS =
             "assist_handles_suppress_on_apps";
 
+    /**
+     * Allow touch passthrough above assist area during a session.
+     */
+    public static final String ASSIST_TAP_PASSTHROUGH = "assist_tap_passthrough";
+
     private SystemUiDeviceConfigFlags() { }
 }