Add original artifact name to TransformerContext

[grossws]

Shadow Version

5.2.0

Gradle Version

6.1.1

Currently TransformerContext only relative path. For some transformers it would be helpful to have not only relative path but original artifact name to base decisions on that.

In my case I want to merge some files in particular order when assembling uber-jar to allow overriding configuration values in current artifact to be last in the merge. It's similar to how current AppendingTransformer works but with deferred joining. Then with current project dependency tree I can topologically sort entries before actually merging them.

If you have some other ideas how to get the same result without extending transformer context I'm eager to listen.

[Goooler]

Will track discussions and details in #913.

[Goooler]

My bad, reopen this as you requested to add the original jar names in TransformerContext instead of FileTreeElement, which is related to #913.