Fix Remote Config pre-configure access.

Currently, when `RemoteConfig.remoteConfig()` is called before
`FirebaseApp.configure()` is called, Similar to Database, AppCheck, and
others we'll now throw an ObjC exception. We're not going to make it
nullable or throw a Swift compatible error since it'd affect the
callsite of every usage (either a `?` or `try`) and this is deemed a
programming error: `configure()` has to be called first.

Fixes #8640

FirebaseRemoteConfig/Sources/FIRRemoteConfig.m

@@ -78,10 +78,12 @@ + (nonnull FIRRemoteConfig *)remoteConfigWithApp:(FIRApp *_Nonnull)firebaseApp {
 
 + (nonnull FIRRemoteConfig *)remoteConfigWithFIRNamespace:(NSString *_Nonnull)firebaseNamespace {
   if (![FIRApp isDefaultAppConfigured]) {
-    FIRLogError(kFIRLoggerRemoteConfig, @"I-RCN000047",
-                @"FIRApp not configured. Please make sure you have called [FIRApp configure]");
-    // TODO: Maybe throw an exception here? That'd be a breaking change though, but at this point
-    // RC can't work as expected.
+    [NSException raise:@"FIRAppNotConfigured"
+                format:@"The default `FirebaseApp` instance must be configured before the "
+                       @"default Remote Config instance can be initialized. One way to ensure this "
+                       @"is to call `FirebaseApp.configure()` in the App Delegate's "
+                       @"`application(_:didFinishLaunchingWithOptions:)` or the `@main` struct's "
+                       @"initializer in SwiftUI."];
   }
 
   return [FIRRemoteConfig remoteConfigWithFIRNamespace:firebaseNamespace app:[FIRApp defaultApp]];
@@ -99,10 +101,12 @@ + (nonnull FIRRemoteConfig *)remoteConfigWithFIRNamespace:(NSString *_Nonnull)fi
 + (FIRRemoteConfig *)remoteConfig {
   // If the default app is not configured at this point, warn the developer.
   if (![FIRApp isDefaultAppConfigured]) {
-    FIRLogError(kFIRLoggerRemoteConfig, @"I-RCN000047",
-                @"FIRApp not configured. Please make sure you have called [FIRApp configure]");
-    // TODO: Maybe throw an exception here? That'd be a breaking change though, but at this point
-    // RC can't work as expected.
+    [NSException raise:@"FIRAppNotConfigured"
+                format:@"The default `FirebaseApp` instance must be configured before the "
+                       @"default Remote Config instance can be initialized. One way to ensure this "
+                       @"is to call `FirebaseApp.configure()` in the App Delegate's "
+                       @"`application(_:didFinishLaunchingWithOptions:)` or the `@main` struct's "
+                       @"initializer in SwiftUI."];
   }
 
   return [FIRRemoteConfig remoteConfigWithFIRNamespace:FIRNamespaceGoogleMobilePlatform