webkit: SystemImpl: Make systemIsDebuggable() check IS_ENG as well

* Since we are shipping userdebug builds by default
  it'd be nice to keep signature and version downgrade
  checks intact.
* Fixes : https://gitlab.com/LineageOS/issues/android/-/issues/2192

Change-Id: Ib46ccb50ac091469caf99a73a5a08942cbc457f6

services/core/java/com/android/server/webkit/SystemImpl.java

@@ -219,7 +219,7 @@ public class SystemImpl implements SystemInterface {
 
     @Override
     public boolean systemIsDebuggable() {
-        return Build.IS_DEBUGGABLE;
+        return Build.IS_DEBUGGABLE && Build.IS_ENG;
     }
 
     @Override