Generates InjectedTest in a named package.

[Vlatombe]

This makes the test friendlier to JUnit results collection when working with PCT or in multi-module projects in general.

The package name is derived from groupId and artifactId, but can also be provided through configuration if needed.

Testing done

Existing IT parent-4x exercises this, though doesn't make any assertion about the actual package name being used. Could add a new one if needed.

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[basil]

+1, seems reasonable to use a unique name for each plugin to facilitate test result visualizations.

[jglick]

Looks helpful. Should not break any tools which run -Dtest=InjectedTest since that will match a test inside a package.