Add iOS boilerplate to keep pub publish happy

Despite being an Android-only plugin, pub publish has taken it upon
itself to reject any apps that do not include boilerplate iOS
scaffolding, regardless of whether iOS is supported or not.

This is supposed to be 'fixed' in the upcoming 1.20.0 release, but it
makes little sense to constrain the plugin to a release that hasn't even
happened yet.

Rip this back out once Flutter behaves the way it should have from the
beginning.

Author: pmundt

ios/.gitignore

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+.idea/
+.vagrant/
+.sconsign.dblite
+.svn/
+
+.DS_Store
+*.swp
+profile
+
+DerivedData/
+build/
+GeneratedPluginRegistrant.h
+GeneratedPluginRegistrant.m
+
+.generated/
+
+*.pbxuser
+*.mode1v3
+*.mode2v3
+*.perspectivev3
+
+!default.pbxuser
+!default.mode1v3
+!default.mode2v3
+!default.perspectivev3
+
+xcuserdata
+
+*.moved-aside
+
+*.pyc
+*sync/
+Icon?
+.tags*
+
+/Flutter/Generated.xcconfig
+/Flutter/flutter_export_environment.sh

ios/Assets/.gitkeep

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+#import <Flutter/Flutter.h>
+
+@interface FlutterWindowmanagerPlugin : NSObject<FlutterPlugin>
+@end

ios/Classes/FlutterWindowmanagerPlugin.h

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+#import "FlutterWindowmanagerPlugin.h"
+#if __has_include(<flutter_windowmanager/flutter_windowmanager-Swift.h>)
+#import <flutter_windowmanager/flutter_windowmanager-Swift.h>
+#else
+// Support project import fallback if the generated compatibility header
+// is not copied when this plugin is created as a library.
+// https://forums.swift.org/t/swift-static-libraries-dont-copy-generated-objective-c-header/19816
+#import "flutter_windowmanager-Swift.h"
+#endif
+
+@implementation FlutterWindowmanagerPlugin
++ (void)registerWithRegistrar:(NSObject<FlutterPluginRegistrar>*)registrar {
+  [SwiftFlutterWindowmanagerPlugin registerWithRegistrar:registrar];
+}
+@end

ios/Classes/FlutterWindowmanagerPlugin.m

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+import Flutter
+import UIKit
+
+public class SwiftFlutterWindowmanagerPlugin: NSObject, FlutterPlugin {
+  public static func register(with registrar: FlutterPluginRegistrar) {
+    let channel = FlutterMethodChannel(name: "flutter_windowmanager", binaryMessenger: registrar.messenger())
+    let instance = SwiftFlutterWindowmanagerPlugin()
+    registrar.addMethodCallDelegate(instance, channel: channel)
+  }
+
+  public func handle(_ call: FlutterMethodCall, result: @escaping FlutterResult) {
+    result("iOS " + UIDevice.current.systemVersion)
+  }
+}

ios/Classes/SwiftFlutterWindowmanagerPlugin.swift

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+#
+# To learn more about a Podspec see http://guides.cocoapods.org/syntax/podspec.html.
+# Run `pod lib lint flutter_windowmanager.podspec' to validate before publishing.
+#
+Pod::Spec.new do |s|
+  s.name             = 'flutter_windowmanager'
+  s.version          = '0.0.1'
+  s.summary          = 'A new flutter plugin project.'
+  s.description      = <<-DESC
+A new flutter plugin project.
+                       DESC
+  s.homepage         = 'http://example.com'
+  s.license          = { :file => '../LICENSE' }
+  s.author           = { 'Your Company' => '[email protected]' }
+  s.source           = { :path => '.' }
+  s.source_files = 'Classes/**/*'
+  s.dependency 'Flutter'
+  s.platform = :ios, '8.0'
+
+  # Flutter.framework does not contain a i386 slice. Only x86_64 simulators are supported.
+  s.pod_target_xcconfig = { 'DEFINES_MODULE' => 'YES', 'VALID_ARCHS[sdk=iphonesimulator*]' => 'x86_64' }
+  s.swift_version = '5.0'
+end