[MNG-7921] Allow plugins to control classpath extensions

**[Dave Syer](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=david_syer)** opened **[MNG-7921](https://issues.apache.org/jira/browse/MNG-7921?redirect=false)** and commented

It's great that a plugin (or extension jar) can have `` (specifically I want to use Google Guice in a plugin and this seems to be the only way), but it can only be applied globally AFAIK, so all plugins get the same exported packages and there might consequently be conflicts. It would be nice if a plugin that declared it was an extension could elect to specify exported packages independent of other plugins.

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**Affects:** 3.9.5

**Attachments:**
- [image-2024-06-30-19-37-28-275.png](https://issues.apache.org/jira/secure/attachment/13069872/image-2024-06-30-19-37-28-275.png) (_152.85 kB_)

**Issue Links:**
- [MNG-7955](https://issues.apache.org/jira/browse/MNG-7955) Plugins should be allowed some control over the imported packages