Introduce Build.VERSION.KNOWN_CODENAMES.

See go/mainline-sdk-codenames-issue.

Known values are to be used to distinguish multiple pre-release
codenames, and to allow in development artifacts to be installable
on released versions of the platform for testing going forward.

This does not change pre-T behaviour at large however.

Bug: 211747008
Test: presubmit
Change-Id: I0c8df8e767ea61b27bb53da53fb6c9b2c842dbbc

core/api/system-current.txt

@@ -7829,6 +7829,7 @@ package android.os {
   }
 
   public static class Build.VERSION {
+    field @NonNull public static final java.util.Set<java.lang.String> KNOWN_CODENAMES;
     field @NonNull public static final String PREVIEW_SDK_FINGERPRINT;
   }
 

core/java/android/os/Build.java

@@ -31,6 +31,7 @@ import android.sysprop.DeviceProperties;
 import android.sysprop.SocProperties;
 import android.sysprop.TelephonyProperties;
 import android.text.TextUtils;
+import android.util.ArraySet;
 import android.util.Slog;
 import android.view.View;
 
@@ -39,6 +40,7 @@ import dalvik.system.VMRuntime;
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Objects;
+import java.util.Set;
 import java.util.stream.Collectors;
 
 /**
@@ -396,6 +398,17 @@ public class Build {
          */
         public static final String CODENAME = getString("ro.build.version.codename");
 
+        /**
+         * All known codenames starting from {@link VERSION_CODES.Q}.
+         *
+         * <p>This includes in development codenames as well.
+         *
+         * @hide
+         */
+        @SystemApi
+        @NonNull public static final Set<String> KNOWN_CODENAMES =
+                new ArraySet<>(new String[]{"Q", "R", "S", "Sv2", "Tiramisu"});
+
         private static final String[] ALL_CODENAMES
                 = getStringList("ro.build.version.all_codenames", ",");