Add testing of CDI behaviors

[joakime]

We currently have in the jetty-9.4.x branch 3 different ways to use CDI.

1. There's the built into the webapp approach where weld is included as a library in the WEB-INF/lib
2. There's the old CDI 1 server side setup / behaviors from the jetty-cdi top level module
3. There's the new CDI 2 server side setup / behaviors introduced from issue Update to CDI 2.0 for cdi module #1900

Now that we have a /tests/test-distribution/ module, we should make sure that the various behaviors still work, or remove them (I suspect that the server side CDI 1 behavior has no reason to exist anymore as the server side CDI 2 behaviors should be backwards compatible)

[joakime]

Opened PR #3737

@janbartel would you be ok with me deleting the old, CDI1, long since deprecated jetty-cdi stuff? it was experimental, and doesn't work anyway.
I would leave the cdi2 module, but expand on it slightly to include some extra [depends], and fix the XML that updates the WebAppClassLoader.

[joakime]

Merged PR #3737