Add list of all providers in their basic form for convenience

Author: SUPERCILEX

auth/README.md

@@ -156,6 +156,9 @@ startActivityForResult(
     RC_SIGN_IN);
 ```
 
+To enable all supported providers in their basic configuration,
+use `setProviders(AuthUI.ALL_PROVIDERS)`
+
 If a terms of service URL and a custom theme are required:
 
 ```java

auth/src/main/java/com/firebase/ui/auth/AuthUI.java

@@ -265,6 +265,16 @@ public class AuthUI {
                     TWITTER_PROVIDER
             )));
 
+    /**
+     * The list of all supported authentication providers in Firebase Auth UI in their basic
+     * {@link IdpConfig} form.
+     */
+    public static final List<IdpConfig> ALL_PROVIDERS =
+            Arrays.asList(new AuthUI.IdpConfig.Builder(AuthUI.EMAIL_PROVIDER).build(),
+                          new AuthUI.IdpConfig.Builder(AuthUI.GOOGLE_PROVIDER).build(),
+                          new AuthUI.IdpConfig.Builder(AuthUI.FACEBOOK_PROVIDER).build(),
+                          new AuthUI.IdpConfig.Builder(AuthUI.TWITTER_PROVIDER).build());
+
     private static final IdentityHashMap<FirebaseApp, AuthUI> INSTANCES = new IdentityHashMap<>();
 
     private final FirebaseApp mApp;