fix(ui): Web recaptcha hover removed after use. (#8812)

Fixes #4377

After showing a recaptcha in web for SMS login, the recaptcha icon
overlay persists on the app until it is reloaded, often blocking an
app's buttons and other interactive widgets. This adds removal of the
web UI element in the clear method, and ensures that clear is called on
any RecaptchaVerifier() objects created by flutterfire.

packages/firebase_auth/firebase_auth/lib/src/firebase_auth.dart

@@ -604,12 +604,16 @@ class FirebaseAuth extends FirebasePluginPlatform {
     RecaptchaVerifier? verifier,
   ]) async {
     assert(phoneNumber.isNotEmpty);
-
+    // If we add a recaptcha to the page by creating a new instance, we must
+    // also clear that instance before proceeding.
+    bool mustClear = verifier == null;
     verifier ??= RecaptchaVerifier();
-    return ConfirmationResult._(
-      this,
-      await _delegate.signInWithPhoneNumber(phoneNumber, verifier.delegate),
-    );
+    final result =
+        await _delegate.signInWithPhoneNumber(phoneNumber, verifier.delegate);
+    if (mustClear) {
+      verifier.clear();
+    }
+    return ConfirmationResult._(this, result);
   }
 
   /// Authenticates a Firebase client using a popup-based OAuth authentication

packages/firebase_auth/firebase_auth/lib/src/user.dart

@@ -259,11 +259,16 @@ class User {
     RecaptchaVerifier? verifier,
   ]) async {
     assert(phoneNumber.isNotEmpty);
+    // If we add a recaptcha to the page by creating a new instance, we must
+    // also clear that instance before proceeding.
+    bool mustClear = verifier == null;
     verifier ??= RecaptchaVerifier();
-    return ConfirmationResult._(
-      _auth,
-      await _delegate.linkWithPhoneNumber(phoneNumber, verifier.delegate),
-    );
+    final result =
+        await _delegate.linkWithPhoneNumber(phoneNumber, verifier.delegate);
+    if (mustClear) {
+      verifier.clear();
+    }
+    return ConfirmationResult._(_auth, result);
   }
 
   /// Re-authenticates a user using a fresh credential.

packages/firebase_auth/firebase_auth_web/lib/src/firebase_auth_web_recaptcha_verifier_factory.dart

@@ -117,7 +117,8 @@ class RecaptchaVerifierFactoryWeb extends RecaptchaVerifierFactoryPlatform {
 
   @override
   void clear() {
-    return _delegate.clear();
+    _delegate.clear();
+    window.document.getElementById(_kInvisibleElementId)?.remove();
   }
 
   @override