[espresso] Adds EspressoFlutter as a first-party plugin

[collinjackson]

Description

Initial open source release of Espresso bindings for Flutter as a new first-party plugin, espresso.

Related Issues

Fixes flutter/flutter#38983

flutter/flutter#32062
flutter/flutter#32987
flutter/flutter#31670

Checklist

Before you create this PR confirm that it meets all requirements listed below by checking the relevant checkboxes ([x]). This will ensure a smooth and quick review process.

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• My PR includes unit or integration tests for all changed/updated/fixed behaviors (See Contributor Guide).
• All existing and new tests are passing.
• I updated/added relevant documentation (doc comments with ///).
• The analyzer (flutter analyze) does not report any problems on my PR.
• I read and followed the Flutter Style Guide.
• The title of the PR starts with the name of the plugin surrounded by square brackets, e.g. [shared_preferences]
• I updated pubspec.yaml with an appropriate new version according to the pub versioning philosophy.
• I updated CHANGELOG.md to add a description of the change.
• I signed the CLA.
• I am willing to follow-up on review comments in a timely manner.

Breaking Change

Does your PR require plugin users to manually update their apps to accommodate your change?

• Yes, this is a breaking change (please indicate a breaking change in CHANGELOG.md and increment major revision).
• No, this is not a breaking change.

[adazh]

Wow~ This is huge! Thank you Collin for all the efforts in open sourcing the Espresso-Flutter library!!!

[rfitz123]

Does this plugin support test recording?

[diegobarle]

I've tried to record an Espresso Test but the clicks and actions done in the device are not being recorded. Record Espresso Test works for normal Android apps but when an app is created using Flutter, it seems like the recorder is unable to recognise taps. You can add assertions using the assertions window but it's not much use without being able to record the navigation through the app.

[✓] Flutter (Channel stable, 2.2.3, on Mac OS X 10.15.7 19H1217 darwin-x64, locale en-GB)
[✓] Android toolchain - develop for Android devices (Android SDK version 30.0.2)
[✓] Xcode - develop for iOS and macOS
[✓] Chrome - develop for the web
[✓] Android Studio (version 4.1)
[✓] VS Code (version 1.58.2)
[✓] Connected device (4 available)

• No issues found!