Define plat_file_contexts_cts for testAospFileContexts

A new variant of plat_file_contexts is introduced which does not
contain any extra file_contexts such as overlay or asan entries.

Bug: 394725259
Test: atest CtsSecurityHostTestCases
Change-Id: I970be3467d5514571b6ec4630eb64dd84fe0f1c4
diff --git a/contexts/Android.bp b/contexts/Android.bp
index 638f202..cf7c175 100644
--- a/contexts/Android.bp
+++ b/contexts/Android.bp
@@ -87,6 +87,14 @@
     },
 }
 
+// The platform file context without any extra added. This is used by CTS to
+// ensure that no entries are removed from the AOSP file.
+file_contexts {
+    name: "plat_file_contexts_cts",
+    defaults: ["contexts_flags_defaults"],
+    srcs: [":file_contexts_files{.plat_private}"],
+}
+
 file_contexts {
     name: "plat_file_contexts.recovery",
     defaults: ["contexts_flags_defaults"],