Add KeyChainService credential management app APIs

Background
* This is part of the work to support
  a credential management app on
  unmanaged devices.
Changes
* Add KeyChainService API methods to
  modify the stored credential management app.

Manual Testing
* Install TestDPC
* Request to manage credentials (fire intent).
  Add policy mapping: 'com.android.chrome' ->
  'client.badssl.com:443' -> 'testAlias'
* Install badssl user certificate as credential
  management app (TestDPC). Set alias to 'testAlias'
* Check certificate is installed in Settings
* Go to chrome > client.badssl.com
* Verify no certificate selection prompt is
  displayed. User is automatically authenticated.
* Remove credential management app from Settings
  Security > Encryption and credentials >
  Certificate management app
* Verify credential management app is removed and
  'testAlias' is uninstalled.

Bug: 165641221
Test: Manual Testing
      atest com.android.keychain.KeyChainServiceRoboTest

Change-Id: I00b7df27a92f6ee4f74546f892c83290fead1112

keystore/java/android/security/AppUriAuthenticationPolicy.java

@@ -28,8 +28,10 @@ import org.xmlpull.v1.XmlSerializer;
 
 import java.io.IOException;
 import java.util.HashMap;
+import java.util.HashSet;
 import java.util.Map;
 import java.util.Objects;
+import java.util.Set;
 
 /**
  * The app-URI authentication policy is set by the credential management app. This policy determines
@@ -223,4 +225,17 @@ public final class AppUriAuthenticationPolicy implements Parcelable {
         }
     }
 
+    /**
+     * Get the set of aliases found in the policy.
+     *
+     * @hide
+     */
+    public Set<String> getAliases() {
+        Set<String> aliases = new HashSet<>();
+        for (UrisToAliases appsToUris : mAppToUris.values()) {
+            aliases.addAll(appsToUris.getUrisToAliases().values());
+        }
+        return aliases;
+    }
+
 }