chore(messaging): add no-op ios podspec for web plugin

Author: Salakar

packages/firebase_messaging/firebase_messaging_web/ios/firebase_messaging_web.podspec

@@ -0,0 +1,23 @@
+#
+# To learn more about a Podspec see http://guides.cocoapods.org/syntax/podspec.html
+#
+
+# An iOS directory and podspec is required for Flutter versions < 1.20.0
+Pod::Spec.new do |s|
+    s.name             = 'firebase_messaging_web'
+    s.version          = '0.1.0'
+    s.summary          = 'No-op implementation of firebase_messaging_web web plugin to avoid build issues on iOS'
+    s.description      = <<-DESC
+  temp fake firebase_messaging_web plugin
+                         DESC
+    s.homepage         = 'https://github.com/FirebaseExtended/flutterfire/tree/master/packages/firebase_messaging/firebase_messaging_web'
+    s.license          = { :file => '../LICENSE' }
+    s.author           = { 'Flutter Team' => '[email protected]' }
+    s.source           = { :path => '.' }
+    s.source_files = 'Classes/**/*'
+    s.public_header_files = 'Classes/**/*.h'
+    s.dependency 'Flutter'
+
+    s.ios.deployment_target = '8.0'
+  end
+