[MSHADE-411] When Shade finds overlapping classes, clarify which class is added to final artifact

**[John Hendrikx](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=john16384)** opened **[MSHADE-411](https://issues.apache.org/jira/browse/MSHADE-411?redirect=false)** and commented

For example:

[WARNING] mediasystem-jfx-2.0.0-SNAPSHOT.jar, javafx-controls-16-win.jar define 5 overlapping classes:

[WARNING] - javafx.scene.control.skin.SpinnerSkin$2

[WARNING] - javafx.scene.control.skin.SpinnerSkin

[WARNING] - javafx.scene.control.skin.SpinnerSkin$1

[WARNING] - javafx.scene.control.skin.SpinnerSkin$4

[WARNING] - javafx.scene.control.skin.SpinnerSkin$3

Here I purposely override the SpinnerSkin class to fix a bug. But it is unclear which version eventually will make it in the uber.jar (I'm hoping it takes it from the first jar listed).

I could not find anything on the website, faq, stackoverflow that clarifies **which** version of the class gets included.

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No further details from [MSHADE-411](https://issues.apache.org/jira/browse/MSHADE-411?redirect=false)

Start with the code path that emits the overlapping-classes warning for the shaded uber-JAR, and trace how duplicate classes are selected. Check the existing Maven Shade Plugin documentation and tests for any stated ordering behavior. Done should make the selected class unambiguous to users and document the relevant behavior.

Written by the indexing model from the issue text.