Enhanced maven-dependency-tree to allow resolution of reactor dependencies

Added an overloaded method to DependencyGraphBuilder that accepts the reactor projects and resolves dependencies from within the reactor.

- Added multi-module-test to validate that the new method works against both direct and transitive deps.
- Added multi-module-plugin to be used to validate multi-module-test
- Added ProjectReferenceKeyGenerator as there is currently no public method to generate the key for MavenProject#projectReferences, MavenSession#projectMap or the Map of reactor projects that we will use.
- Separated the reflective invocation out into the Invoker class.