[flutter_plugin_tools] Include examples in test

[stuartmorgan]

Includes any Dart unit tests for examples when running Dart unit tests
via test.

Also updates the deprecated dart pub run test to dart run test.

Fixes flutter/flutter#102845

Pre-launch Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the Tree Hygiene wiki 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/plugins repo does use dart format.)
• I signed the CLA.
• The title of the PR starts with the name of the plugin surrounded by square brackets, e.g. [shared_preferences]
• I listed 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.
• 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.

[fluttergithubbot]

This pull request is not suitable for automatic merging in its current state.

• The status or check suite android-platform_tests has failed. Please fix the issues identified (or deflake) before re-applying this label.
• The status or check suite android-platform_tests has failed. Please fix the issues identified (or deflake) before re-applying this label.
• The status or check suite android-platform_tests has failed. Please fix the issues identified (or deflake) before re-applying this label.
• The status or check suite android-platform_tests has failed. Please fix the issues identified (or deflake) before re-applying this label.
• The status or check suite android-platform_tests has failed. Please fix the issues identified (or deflake) before re-applying this label.
• The status or check suite android-platform_tests has failed. Please fix the issues identified (or deflake) before re-applying this label.
• The status or check suite android-build_all_plugins has failed. Please fix the issues identified (or deflake) before re-applying this label.
• The status or check suite darwin-lint_podspecs has failed. Please fix the issues identified (or deflake) before re-applying this label.
• The status or check suite ios-build_all_plugins has failed. Please fix the issues identified (or deflake) before re-applying this label.
• The status or check suite ios-build_all_plugins has failed. Please fix the issues identified (or deflake) before re-applying this label.
• The status or check suite ios-platform_tests has failed. Please fix the issues identified (or deflake) before re-applying this label.
• The status or check suite ios-platform_tests has failed. Please fix the issues identified (or deflake) before re-applying this label.

[ditman]

Network on the test runners seems to be flaking:

> Could not GET 'https://dl.google.com/dl/android/maven2/com/android/tools/build/gradle/3.3.0/gradle-3.3.0.pom'. Received status code 502 from server: Bad Gateway

- ERROR | [iOS] unknown: Encountered an unknown error ([!] /usr/bin/curl -f -L -o /var/folders/tn/f_9sf1xx5t14qm_6f83q3b840000gn/T/d20220502-2446-h8f1tx/file.tgz https://dl.google.com/dl/cpdc/ea79acddddcfc5ac/GoogleMaps-4.1.0.tar.gz --create-dirs --netrc-optional --retry 2 -A 'CocoaPods/1.11.2 cocoapods-downloader/1.5.1'

(... restarted all tests after a while)

[ditman]

Everything is passing now, but main is in a small pickle with dependabot