Issue title: Jetty-12 EE10 Default Servlet 
 Issue body: **Target Jetty version(s)**

Jetty-12

**Enhancement Description**

Fix/implement the deficiencies of the ee10 DefaultServlet and ResourceHandler as identified by reviews of #8276: specifically:
 + undisable the `DefaultServletTest` and fix them
 + remove the Generic request/response abstraction
 + javadoc

 Comments: 
 Comment 0: This is mostly done so far.
Most of the remaining work is in the core `ResourceService`
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