Add a Java backend for android.hardware.graphics.common AIDL

This will allow SysUI to access the same struct (in
I27f119f927b23052c5fd8f068cbca75338fe7b91) that HWC uses to describe
its support for DISPLAY_DECORATION.

@hide each API individually. SysUI can access hidden APIs. Otherwise
leave the AIDL files are unchanged.

Bug: 216644902
Test: make
Change-Id: Id33f76e4c55b22d007c7e2314a4dfb778562bace
diff --git a/graphics/common/aidl/Android.bp b/graphics/common/aidl/Android.bp
index 69ee498..d44252a 100644
--- a/graphics/common/aidl/Android.bp
+++ b/graphics/common/aidl/Android.bp
@@ -25,7 +25,8 @@
     ],
     backend: {
         java: {
-            enabled: false,
+            enabled: true,
+            platform_apis: true,
         },
         cpp: {
             enabled: false,