Convert DisplayList to a value-type wrapper

Make DisplayList its own type instead of an alias,
pushing the Skia aspect behind it mostly. Removes a bunch
of manual memory management and opens the door to DisplayList
being a union type with multiple implementations

Test: builds (somehow), boots, hwuiunit passes, CtsUiRendering passes
Change-Id: I1d7806aa3afc5d9ece08b06959920078a5814c59
diff --git a/libs/hwui/jni/GraphicsJNI.h b/libs/hwui/jni/GraphicsJNI.h
index 541d5a5..ba407f2 100644
--- a/libs/hwui/jni/GraphicsJNI.h
+++ b/libs/hwui/jni/GraphicsJNI.h
@@ -24,6 +24,7 @@
 namespace skia {
     class BitmapRegionDecoder;
 }
+class Canvas;
 class Paint;
 struct Typeface;
 }