This PR adds initial support for Swift Package Manager (SPM). Users must opt in. Only compatible with Xcode 15+.
Fixes https://github.com/flutter/flutter/issues/146369.
## Included Features
This PR includes the following features:
* Enabling SPM via config
`flutter config --enable-swift-package-manager`
* Disabling SPM via config (will disable for all projects)
`flutter config --no-enable-swift-package-manager`
* Disabling SPM via pubspec.yaml (will disable for the specific project)
```
flutter:
disable-swift-package-manager: true
```
* Migrating existing apps to add SPM integration if using a Flutter plugin with a Package.swift
* Generates a Swift Package (named `FlutterGeneratedPluginSwiftPackage`) that handles Flutter SPM-compatible plugin dependencies. Generated package is added to the Xcode project.
* Error parsing of common errors that may occur due to using CocoaPods and Swift Package Manager together
* Tool will print warnings when using all Swift Package plugins and encourage you to remove CocoaPods
This PR also converts `integration_test` and `integration_test_macos` plugins to be both Swift Packages and CocoaPod Pods.
## How it Works
The Flutter CLI will generate a Swift Package called `FlutterGeneratedPluginSwiftPackage`, which will have local dependencies on all Swift Package compatible Flutter plugins.
The `FlutterGeneratedPluginSwiftPackage` package will be added to the Xcode project via altering of the `project.pbxproj`.
In addition, a "Pre-action" script will be added via altering of the `Runner.xcscheme`. This script will invoke the flutter tool to copy the Flutter/FlutterMacOS framework to the `BUILT_PRODUCTS_DIR` directory before the build starts. This is needed because plugins need to be linked to the Flutter framework and fortunately Swift Package Manager automatically uses `BUILT_PRODUCTS_DIR` as a framework search path.
CocoaPods will continue to run and be used to support non-Swift Package compatible Flutter plugins.
## Not Included Features
It does not include the following (will be added in future PRs):
* Create plugin template
* Create app template
* Add-to-App integration
Pre work for https://github.com/flutter/engine/pull/51229. Removes a lot of code referencing v1 of the android embedding, though not necessarily all of it (I may have missed some, it is hard to know).
Will hopefully make landing that PR less painful (or maybe painless?)
Part of https://github.com/flutter/flutter/issues/130277
Without this, if a user runs an app that has plugins that call method channels with the `preview` device, the app will build successfully, however, they will get a runtime error when their dart code tries to call the method channel that does not exist in the native build (which was pre-built and thus does not include the plugin code).
This change adds a validation when injecting plugins that will tool exit if the device-id is `preview` and their project contains plugins with method channels.
