Break a dependency of libui on libandroid

This was only a header dependency, but it still
created a circular dependency, which will cause
problems in another CL.

We fix this by creating a libarect static library
containing only that header. both libui and
libandroid now depend on it and reexport the 
header. 

We also make sure rect.h ends-up in the right
place.

Test: built and booted device
Bug: 35164655

Change-Id: Iba25b8b801b26b26ec1401c00caf367a06f197ca
diff --git a/libs/ui/Android.bp b/libs/ui/Android.bp
index cfe170d..ea18644 100644
--- a/libs/ui/Android.bp
+++ b/libs/ui/Android.bp
@@ -75,6 +75,12 @@
         "libutils",
         "liblog",
     ],
+
+    static_libs: [
+        "libarect",
+    ],
+
+    export_static_lib_headers: ["libarect"],
 }
 
 subdirs = ["tests"]