WIP: feat(appcheck): Implement initial reCAPTCHA Enterprise provider

This commit introduces the basic structure for the reCAPTCHA Enterprise
App Check provider. It's currently a work in progress and not yet ready
for review or final integration.

- Added `RecaptchaEnterpriseAppCheckProviderFactory`.
- Added `FirebaseAppCheckRecaptchaEnterpriseRegistrar`.
- Further implementation and testing are required.

Author: hiteshmaurya56

appcheck/firebase-appcheck-recaptchaenterprise/src/main/java/com/google/firebase/appcheck/recaptchaenterprise/FirebaseAppCheckRecaptchaEnterpriseRegistrar.java

@@ -0,0 +1,70 @@
+package com.google.firebase.appcheck.recaptchaenterprise;
+
+import android.app.Application;
+import android.content.Context;
+
+import com.google.android.gms.common.annotation.KeepForSdk;
+import com.google.firebase.FirebaseApp;
+import com.google.firebase.annotations.concurrent.Blocking;
+import com.google.firebase.annotations.concurrent.Lightweight;
+import com.google.firebase.appcheck.recaptchaenterprise.internal.RecaptchaEnterpriseAppCheckProvider;
+import com.google.firebase.appcheck.recaptchaenterprise.internal.SiteKey;
+import com.google.firebase.components.Component;
+import com.google.firebase.components.ComponentRegistrar;
+import com.google.firebase.components.Dependency;
+import com.google.firebase.components.Qualified;
+import com.google.firebase.platforminfo.LibraryVersionComponent;
+
+import java.util.Arrays;
+import java.util.List;
+import java.util.concurrent.Executor;
+
+/**
+ * {@link ComponentRegistrar} for setting up FirebaseAppCheck reCAPTCHA Enterprise's dependency
+ * injections in Firebase Android Components.
+ *
+ * @hide
+ */
+@KeepForSdk
+public class FirebaseAppCheckRecaptchaEnterpriseRegistrar implements ComponentRegistrar {
+  private static final String LIBRARY_NAME = "fire-app-check-recaptcha-enterprise";
+
+  @Override
+  public List<Component<?>> getComponents() {
+    Qualified<Executor> liteExecutor = Qualified.qualified(Lightweight.class, Executor.class);
+    Qualified<Executor> blockingExecutor = Qualified.qualified(Blocking.class, Executor.class);
+
+    return Arrays.asList(
+        Component.builder(Application.class)
+            .name(LIBRARY_NAME)
+            .add(Dependency.required(Context.class))
+            .factory(
+                container -> {
+                  Context context = container.get(Context.class);
+                  return (Application) context.getApplicationContext();
+                })
+            .build(),
+        Component.builder(SiteKey.class)
+            .name(LIBRARY_NAME)
+            .factory(
+                container -> new SiteKey(RecaptchaEnterpriseAppCheckProviderFactory.getSiteKey()))
+            .build(),
+        Component.builder(RecaptchaEnterpriseAppCheckProvider.class)
+            .name(LIBRARY_NAME)
+            .add(Dependency.required(FirebaseApp.class))
+            .add(Dependency.required(Application.class))
+            .add(Dependency.required(SiteKey.class))
+            .add(Dependency.required(liteExecutor))
+            .add(Dependency.required(blockingExecutor))
+            .factory(
+                (container ->
+                    new RecaptchaEnterpriseAppCheckProvider(
+                        container.get(FirebaseApp.class),
+                        container.get(Application.class),
+                        container.get(SiteKey.class),
+                        container.get(liteExecutor),
+                        container.get(blockingExecutor))))
+            .build(),
+        LibraryVersionComponent.create(LIBRARY_NAME, BuildConfig.VERSION_NAME));
+  }
+}

appcheck/firebase-appcheck-recaptchaenterprise/src/main/java/com/google/firebase/appcheck/recaptchaenterprise/RecaptchaEnterpriseAppCheckProviderFactory.java

@@ -0,0 +1,44 @@
+package com.google.firebase.appcheck.recaptchaenterprise;
+
+import androidx.annotation.NonNull;
+import com.google.firebase.FirebaseApp;
+import com.google.firebase.appcheck.AppCheckProvider;
+import com.google.firebase.appcheck.AppCheckProviderFactory;
+import com.google.firebase.appcheck.FirebaseAppCheck;
+import com.google.firebase.appcheck.recaptchaenterprise.internal.RecaptchaEnterpriseAppCheckProvider;
+
+/**
+ * Implementation of an {@link AppCheckProviderFactory} that builds <br>
+ * {@link RecaptchaEnterpriseAppCheckProvider}s. This is the default implementation.
+ */
+public class RecaptchaEnterpriseAppCheckProviderFactory implements AppCheckProviderFactory {
+
+  private static volatile RecaptchaEnterpriseAppCheckProviderFactory instance;
+  private static String siteKey;
+
+  /** Gets an instance of this class for installation into a {@link FirebaseAppCheck} instance. */
+  @NonNull
+  public static RecaptchaEnterpriseAppCheckProviderFactory getInstance(@NonNull String siteKey) {
+    if (instance == null) {
+      synchronized (RecaptchaEnterpriseAppCheckProviderFactory.class) {
+        if (instance == null) {
+          instance = new RecaptchaEnterpriseAppCheckProviderFactory();
+          RecaptchaEnterpriseAppCheckProviderFactory.siteKey = siteKey;
+        }
+      }
+    }
+    return instance;
+  }
+
+  @NonNull
+  public static String getSiteKey() {
+    return siteKey;
+  }
+
+  @NonNull
+  @Override
+  @SuppressWarnings("FirebaseUseExplicitDependencies")
+  public AppCheckProvider create(@NonNull FirebaseApp firebaseApp) {
+    return firebaseApp.get(RecaptchaEnterpriseAppCheckProvider.class);
+  }
+}