Add tests to ensure the correct arguments are passed to build_runner

[jakemac53]

Original title: webdev serve

passes as an argument to the daemon

This can lead to options skew - it should just be setting the build target and not forwarding this as an argument to the daemon.

[grouma]

Updating bug as we just need to add a test.

[grouma]

These tests were added, e.g.:

webdev/webdev/test/integration_test.dart

Line 22 in a304b5e

test('passing extra args to build fails with bad usage', () async {