Create a version_script to explicitly define exported symbols for libhwui

The linker script defines both the C and C++ headers exported by libhwui
and libskia (included via whole_static_libs).  Reducing the surface
area makes it clear what libhwui's external dependencies are as well
as reducing the binary size by about ~12% (1.04 MB on 64-bit and 789KB
on 32-bit builds for the Pixel 3a in userdebug).

Test: compiles and links
Bug: 150782769
Change-Id: Ia202a12c1605c851c52d953f0db0f4814ade8dfd
diff --git a/libs/hwui/Android.bp b/libs/hwui/Android.bp
index 5c08325..769afc5 100644
--- a/libs/hwui/Android.bp
+++ b/libs/hwui/Android.bp
@@ -603,6 +603,11 @@
         "android_graphics_jni",
     ],
     export_header_lib_headers: ["android_graphics_apex_headers"],
+    target: {
+        android: {
+            version_script: "libhwui.map.txt",
+        }
+    },
 }
 
 cc_library_static {