If xcode_backend.sh script fails or substitute variables are missing, fail the host Xcode build (#37449)

`flutter build aar`

This new build command works just like `flutter build apk` or `flutter build appbundle`, but for plugin and module projects.

This PR also refactors how plugins are included in app or module projects. By building the plugins as AARs, the Android Gradle plugin is able to use Jetifier to translate support libraries into AndroidX libraries for all the plugin's native code. Thus, reducing the error rate when using AndroidX in apps.

This change also allows to build modules as AARs, so developers can take these artifacts and distribute them along with the native host app without the need of the Flutter tool. This is a requirement for add to app.

`flutter build aar` generates POM artifacts (XML files) which contain metadata about the native dependencies used by the plugin. This allows Gradle to resolve dependencies at the app level. The result of this new build command is a single build/outputs/repo, the local repository that contains all the generated AARs and POM files.

In a Flutter app project, this local repo is used by the Flutter Gradle plugin to resolve the plugin dependencies. In add to app case, the developer needs to configure the local repo and the dependency manually in `build.gradle`:


repositories {
    maven {
        url "<path-to-flutter-module>build/host/outputs/repo"
    }
}

dependencies {
    implementation("<package-name>:flutter_<build-mode>:1.0@aar") {
       transitive = true
    }
}

This reverts commit 11460b83.

`flutter build aar`

This new build command works just like `flutter build apk` or `flutter build appbundle`, but for plugin and module projects.

This PR also refactors how plugins are included in app or module projects. By building the plugins as AARs, the Android Gradle plugin is able to use Jetifier to translate support libraries into AndroidX libraries for all the plugin's native code. Thus, reducing the error rate when using AndroidX in apps.

This change also allows to build modules as AARs, so developers can take these artifacts and distribute them along with the native host app without the need of the Flutter tool. This is a requirement for add to app.

`flutter build aar` generates POM artifacts (XML files) which contain metadata about the native dependencies used by the plugin. This allows Gradle to resolve dependencies at the app level. The result of this new build command is a single build/outputs/repo, the local repository that contains all the generated AARs and POM files.

In a Flutter app project, this local repo is used by the Flutter Gradle plugin to resolve the plugin dependencies. In add to app case, the developer needs to configure the local repo and the dependency manually in `build.gradle`:


repositories {
    maven {
        url "<path-to-flutter-module>build/host/outputs/repo"
    }
}

dependencies {
    implementation("<package-name>:flutter_<build-mode>:1.0@aar") {
       transitive = true
    }
}

Change Xcode project developmentRegion to 'en' and plist CFBundleDevelopmentRegion to DEVELOPMENT_LANGUAGE (#34293)

Disable CocoaPods input and output paths in Xcode build phase and adopt new Xcode build system (#34167)

Updates the Podfile template to use the CocoaPod disable_input_output_paths installation option which prevents the [CP] Embed Pods Frameworks build phase from outputting the Flutter.framework files.

This is a small follow up to the previous AndroidX PR: https://github.com/flutter/flutter/pull/31028

This fixes an issue mentioned [here](https://github.com/flutter/flutter/issues/28805) where the androidX flag for a module is not set when creating a new project:

`flutter create --androidx -t module my_flutter`

This wasn't included originally since it didn't seem to be necessary for
macOS in testing, but not having it breaks Swift plugins. This matches
the iOS Swift Podfile template.

Revert "Disable CocoaPods input and output paths in Xcode build phase and adopt new Xcode build system (#33852)" (#33882)

This reverts commit d053fe5c.

Disable CocoaPods input and output paths in Xcode build phase and adopt new Xcode build system (#33852)

Updates the Podfile template to use the CocoaPod disable_input_output_paths installation option which prevents the [CP] Embed Pods Frameworks build phase from outputting the Flutter.framework files.

Revert "Disable CocoaPods input and output paths in Xcode build phase and adopt new Xcode build system (#33684)"

This reverts commit ef792fc3.

Disable CocoaPods input and output paths in Xcode build phase and adopt new Xcode build system (#33684)

Updates the Podfile template to use the CocoaPod disable_input_output_paths installation option which prevents the [CP] Embed Pods Frameworks build phase from outputting the Flutter.framework files.

Enables the CocoaPods-based plugin workflow for macOS. This allows a
macOS project to automatically fetch and add native plugin
implementations via CocoaPods for anything in pubspec.yaml, as is done
on iOS.

* Updating dart.dev related links

* Update packages/flutter_tools/lib/src/base/context.dart

* Update packages
* Capture JSON RPC errors that presently get swallowed