Update proguard flags.

Fully R8 optimized variants may crash with:
java.lang.AbstractMethodError exception.

Test: build, manual test on device.
Change-Id: I18a7b011ddd3536e3d33b991954a52e5fc5c7d56

proguard.flags

@@ -50,4 +50,13 @@
 -dontwarn android.graphics.**
 
 # Ignore warnings for hidden utility classes referenced from the shared lib
--dontwarn com.android.internal.util.**
+-dontwarn com.android.internal.util.**
+
+################ Do not optimize recents lib #############
+-keep class com.android.systemui.** {
+  *;
+}
+
+-keep class com.android.quickstep.** {
+  *;
+}