Pax Web 9 release with JDK 11 compatibility

[grgrzybek]

This is an issue to discuss a new release of Pax Web based on Pax Web 8 (no new features comparing to version 8), but with new major versions of the runtimes:

• Jetty 10
• Tomcat 9
• Undertow 2.2

Jetty 10 is still an implementation of Servlet API 4, but with minimum JDK 11 requirement. That's the only reason why Pax Web 8 doesn't use Jetty 10.

We can't (yet?) use Tomcat 10, as it's using Jakarta Servlet API 5 (with jakarta.servlet.* package). And it's not that easy - see osgi/osgi#381.

However javax → jakarta package migration impacts more enterprise OSGi specifications and it can't be done step by step. It has to be done all at once.