mvnup: shade-plugin upgrade breaks projects with custom ResourceTransformers #12991

Problem

`mvnup` upgrades `maven-shade-plugin` from 1.3.3 to 3.5.0, which breaks projects that use custom `ResourceTransformer` implementations with dependencies not carried forward in the new version:

```
[ERROR] Failed to execute goal org.apache.maven.plugins:maven-shade-plugin:3.5.0:shade
on project myfaces-extcdi-bundle-jsf12:
Unable to parse configuration of mojo ... for parameter transformer:
Cannot create instance of class org.apache.myfaces.extensions.cdi.maven.BeansXmlTransformer:
org/jdom/JDOMException: org.jdom.JDOMException
```

The custom `BeansXmlTransformer` depends on `org.jdom:jdom` which was a transitive dependency in shade-plugin 1.3.3 but not in 3.5.0. The upgrade silently breaks the project.

Affected project

• `myfaces-extcdi` — uses a custom shade `ResourceTransformer` with jdom dependency

Expected behavior

`mvnup`'s `PluginUpgradeStrategy` should be cautious about upgrading plugins that have custom configurations (custom transformers, custom implementations, project-specific plugin extensions). At minimum, it should:

1. Detect when a shade-plugin configuration references project-specific transformer classes
2. Warn or skip the upgrade in such cases

Context

Data from maven4-testing run #13307 testing `maven-4.0.x` against all Apache projects.