This pattern is problematic when Flutter is ported to build systems
that require each executable end-point to be self-contained (e.g.
Bazel).

* enable lint unnecessary_new

* fix tests

* fix tests

* fix tests

* Upgrade everything except matcher.
* Roll matcher (and test)
* Adjust tests that depend on flutter:test directly to depend on a shim
* Require use of package:test shim and remove other references to package:test

This allows the scheduler library to depend on the services library
and the painting library to depend on the scheduler library without
the services library having to depend on the scheduler library.

While I was at it I also cleaned up some of the binding logic: the
licenses logic can now be overridden (and the test library does so),
and the image cache can now be overridden as well.

Fixes #7503
Fixes #8870

Fixes #8200

This patch improves test coverage for a number of files that had low
coverage. This patch also fixes a few minor bugs found by these tests.