Document how to determine if an app is a flutter app

[reidbaker]

Description of what this PR is changing or adding, and why:

Documents how to tell from a built apk if the app uses flutter.
Internal documentation authored by me can be seen by googlers in go/flutter-android-detection

Issues fixed by this PR (if any):
flutter/flutter/issues/170523

PRs or commits this PR depends on (if any):
n/a

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  of 80 characters or fewer.

[gemini-code-assist]

Summary of Changes

Hello @reidbaker, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request introduces comprehensive documentation within the Android deployment guide, outlining various methods to identify whether an Android application package (APK) is built with Flutter. The added content provides both technical instructions using apkanalyzer to inspect APK contents and manifest, as well as mentions of external non-technical tools, aiming to assist users in recognizing Flutter-based applications.

Highlights

• Identifying Flutter Apps: New documentation has been added detailing methods to determine if an Android APK is a Flutter application.
• Technical Methods: Two technical approaches are provided: a recommended method using apkanalyzer to check for libflutter.so, and a secondary method checking for flutterEmbedding in the manifest with important caveats.
• Non-Technical Options: The documentation also includes non-technical ways to identify Flutter apps, such as using specific tools or websites.

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[gemini-code-assist]

Code Review

This pull request adds valuable documentation on how to determine if an Android app is built with Flutter. The methods described are relevant and useful. My review includes several suggestions to improve formatting, clarity, and adherence to the Google Developer Documentation Style Guide. These changes will make the documentation easier to read and follow.

[flutter-website-bot]

Visit the preview URL for this PR (updated for commit f77ca31):

https://flutter-docs-prod--pr12668-i-170523-document-android-d-91rzmxbn.web.app

[sfshaza2]

In this case, I wish I could turn off the bot, as it isn't adding a lot of clarity.

[sfshaza2]

Suggested change

	Why this works:
	Flutter depends on c++ code that we call the flutter engine. That code in android is bundled as an “.so” native library.
	For the life of flutter that file has been named libflutter.so with the flutter framework and developers dart code being
	combined into libapp.so. Flutter code names this library flutter and java/android tooling renames it with the lib prefix
	and handles library location across architectures. This is what many reverse engineers use to identify flutter apps.
	**Why this works**
	Flutter depends on C++ code used by the Flutter engine. In Android,
	this code is bundled with the Flutter framework and the developer's
	Dart code as a native library called `libflutter.so`.
	The Java/Android tooling renames the `flutter` library with the `lib` prefix
	and handles library location across architectures.
	This is how some reverse engineer an APK to identify it as a Flutter app.

[reidbaker]

In this case, I wish I could turn off the bot, as it isn't adding a lot of clarity.

I thought it was pretty helpful. I adopted most of its suggestions

[sfshaza2]

I'm glad to hear that, Reid. I often find it helpful but, in this case, it needed further work, but it won't let me make changes on top of its changes and that frustrates me. (Since its changes are sometimes just wrong or just don't go far enough, etc.)

[sfshaza2]

lgtm