This reverts commit 59bb2dba.

This reverts commit 0f557e72.

This reverts commit dac1baf4.

This reverts commit 36e3b103 to make the build green.

This reverts commit 25b1d43a.

This reverts commit 05d6b08f.

Gradle projects are evaluated in lexicographical order, and the plugin
projects are at the same level as the :app project, so if a plugin has
a name that comes before 'app' (like, for example, any name that starts
with a capital letter), the plugin project will be evaluated before
:app.

Since :app applies the Flutter Gradle plugin, which tries to
modify the dependencies of the plugin projects, we have a problem if the
plugin projects have already been evaluated. Adding
evaluationDependsOn(':app') to the plugin projects fixes this.

Updated example projects to the latest (plugin-enabled) Gradle build
files.

Also removed two unused imports in `pluginClass.java.tmpl`.

The hello_services example can now be built both for Android and iOS.

Fixes #3833