Add Singleton class to collect and validate test spec metadata.

Bug: 296873595
Test: Manual testing (Will add unit test case in the next change.)
Change-Id: Ic4177c5f76602088d52a31ca8d9fbaa703855837
diff --git a/testing/Android.bp b/testing/Android.bp
index 26a7d93..85e6a8b 100644
--- a/testing/Android.bp
+++ b/testing/Android.bp
@@ -12,6 +12,7 @@
 
     ],
     srcs: [
+        "all_test_specs.go",
         "test_spec.go",
         "init.go",
     ],