Bundle org.eclipse.jetty.websocket.server OSGI metadata exports internal instead of public package

**Jetty version(s)**
12.1.6

**Jetty Environment**
core

**Description**
The Maven artifact jetty-websocket-jetty-server (OSGI Bundle name org.eclipse.jetty.websocket.server) exports the wrong package, making it impossible to use from an Eclipse RCP project.

From the MANIFEST.MF found in the jar file, it exports the internal package, but it doesn't export the actual main package:

```
Export-Package: org.eclipse.jetty.websocket.server.internal;version="12.
 1.6";uses:="org.eclipse.jetty.server,org.eclipse.jetty.websocket.api,or
 g.eclipse.jetty.websocket.common,org.eclipse.jetty.websocket.core,org.e
 clipse.jetty.websocket.core.server"
```

As a result, Eclipse complains about using a non-api package when trying to use the contained types, as per the programming guide (see https://jetty.org/docs/jetty/12.1/programming-guide/server/websocket.html#jetty)

The programming guide says one might only need to depend on the API, but the example code makes use of `WebSocketUpgradeHandler.from` and `ServerWebSocketContainer`, which are in the server jar.

It's also unclear how the artifact relates to the *other* artifact that exposes types of the same name (`jetty-websocket-core-server`), these have correct OSGI metadata, but the documentation doesn't mention these bundles at all.

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