fix(ios, crashlytics): depend on FirebaseCoreExtension (#6352)

Crashlytics uses headers from this extension cocoapod, but it is only brought-in
automatically by Storage and Functions currently. Depend on it directly

#6322 (comment)

Author: mikehardy

packages/crashlytics/RNFBCrashlytics.podspec

@@ -36,6 +36,7 @@ Pod::Spec.new do |s|
 
   # Firebase dependencies
   s.dependency          'Firebase/Crashlytics', firebase_sdk_version
+  s.dependency          'FirebaseCoreExtension', firebase_sdk_version
 
   if defined?($RNFirebaseAsStaticFramework)
     Pod::UI.puts "#{s.name}: Using overridden static_framework value of '#{$RNFirebaseAsStaticFramework}'"