Removes .flutter-plugins reference from example by (0) checking out the stable Flutter branch, (1) deleting the packages/espresso/example/android directory, (2) running (in the packages/espresso directory)

flutter create example --platforms android -a kotlin --org "com.example.espresso_example"

and then (3) manually made the following changes:

• Deleted example/analysis_options.yaml (added by command)
• Deleted example/test/ (added by command)
• Restored example/android/app/src/androidTest (deleted by command)
• Restored example/android/app/src/main/java/com/example/espresso_example/MainActivity.java (deleted by command)
• Reset android:usesCleartextTraffic to be true in example/android/app/src/debug/AndroidManifest.xml
• Added back dependency block to example/android/build.gradle.
• Updated Gradle version from 8.3 to 8.7 (downgraded by the command)
• Added back artifact hub
• Removed template TODOs
• Correct namespace to "com.example.espresso_example"
• Correct manifest label to "espresso_example" to maintain consistency
• Add back gradle.projectsEvaluated block to example/android/build.gradle
• Bump AGP version back up to 8.5.1
• Bump Kotlin version back up to 1.9.0
• Delete MainActivity.java

Part of flutter/flutter#157660.

Pre-launch Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the Tree Hygiene page, which explains my responsibilities.
• I read and followed the relevant style guides and ran the auto-formatter. (Unlike the flutter/flutter repo, the flutter/packages repo does use dart format.)
• I signed the CLA.
• The title of the PR starts with the name of the package surrounded by square brackets, e.g. [shared_preferences]
• I linked to at least one issue that this PR fixes in the description above.
• I updated pubspec.yaml with an appropriate new version according to the pub versioning philosophy, or this PR is exempt from version changes.
• I updated CHANGELOG.md to add a description of the change, following repository CHANGELOG style, or this PR is exempt from CHANGELOG changes.
• I updated/added relevant documentation (doc comments with ///).
• I added new tests to check the change I am making, or this PR is test-exempt.
• All existing and new tests are passing.