Move websocket-util classes into websocket-core

[lachlan-roberts]

• Move the websocket-util classes into websocket-core-common internal package.
• Move the websocket-util-server internal classes into the websocket-core-server API.
• API cleanups of websocket-core
• WebSocketUpgradeHandler now uses the WebSocketMappings and can upgrade to multiple different FrameHandlers.
• WebSocketUpgradeFilter now exists in a jar all by itself.

[lachlan-roberts]

@gregw @sbordet There is still something strange about the websocket structure. The websocket-jetty-common module is really just a private implementation but it leaks a bunch of websocket-core classes in its method signatures. It is used as common implementation between websocket-jetty-server and websocket-jetty-client, you are never expected to directly use classes from websocket-jetty-common. This is different to websocket-core-common, you need to use classes directly from this jar as there is no websocket-core-api.

And there is JPMS warnings because these internal classes from websocket-core-common are in the public signatures of websocket-jetty-common and websocket-javax-common, even though these are really just meant to be internal implementation jars.

[sbordet]

@lachlan-roberts there are a bunch of test failures due to the latest changes.

The reason is that now JPMS module org.eclipse.jetty.websocket.jetty.common is only exported to org.eclipse.jetty.websocket.jetty.client and *-server.

However, there are test classes that are in the org.eclipse.jetty.websocket.jetty.common module, and for tests that's the application Lookup object.

However, classes from that package/module are not exported so the Lookup object has allowedModes=0 (which means no permissions), which means that we get an IllegalAccessException when trying to call findVirtual() to find the @OnMessage method.

[sbordet]

Feels like a JDK bug... I sent an email to jigsaw-dev asking for clarifications.

[sbordet]

@lachlan-roberts jigsaw-dev replied and classes from org.eclipse.jetty.websocket.jetty.common must be exported unconditionally.

I'm making this change and see if the PR builds fine.

[sbordet]

Few nibble to fix.