Going forward, Android support libraries are published on maven (instead of bundling them with the SDK). Many plugins depend on these. To avoid requiring plugin users to add the maven repository to their app this change adds the repository to the template for `flutter create`.

This also bumps the support-annotations dependency to 25.4.0 (which also requires the new maven repository).

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`.

* Revert "use color.shadeXxx instead of color[Xxx] (#8932)"

This reverts commit 578ca0a2.

* Revert "add missing const keyword (#8931)"

This reverts commit fac2fac1.

* Revert "Make min/max fling velocity and min fling distance ScrollPhysics properties (#8928)"

This reverts commit dac80aac.

* Revert "Defer to operating system for whichAll (#8921)"

This reverts commit 14933de9.

* Revert "Update gradle wrapper and build-tools version for flutter create. (#8914)"

This reverts commit deb71cc6.

* Update gradle wrapper and build-tools version.

Tested manually by "flutter create" with Idea "flutter run" and from android studio "run" android app.

* Update com.android.tools.build to 2.3.0

Changed the default build output directory in the new project template
to build/, instead of android/build/ and android/app/build/.

Updated tools to ask the Gradle scripts what the build directory is,
since this is configurable in the build scripts, and we need to know
where the build output actually is.

Silenced output from 'flutter build aot' when invoked from Gradle, since
the output was confusing in this case.

Fixes #8723
Fixes #8656
Fixes #8138

* Make new project template gradle-based for Android.

With this change, the 'new project' template uses the same gradle-based build for Android as the hello_services example. This has some implications on build performance, since we're now building a complete Android app instead of just combining a pre-compiled .dex with the Flutter assets.

The very first build is a little over 2x slower, since it needs to download gradle and build the build scripts before getting to the actual code. Subsequent builds with changes to the code are comparable to the old builds. Null builds are faster. Enabling the gradle daemon speeds up subsequent builds by around 5s.

* Move Flutter Gradle plugin to Flutter root.

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

Fixes #3833