chore(implementation)!: use Jetty-12 core without servlets

Port the invoker to upgrade to Eclipse Jetty-12 version 12.  Specifically using the new core APIs of Eclipse Jetty-12 that allow the overhead of a Servlet container to be avoided.   Several optimizations are included, including the optimization that small writes can be buffered in such a way to avoid chunked responses when possible.

BREAKING CHANGE: use Java 17 or above, as required by Eclipse Jetty-12.

invoker/core/src/test/java/com/google/cloud/functions/invoker/IntegrationTest.java

@@ -382,6 +382,9 @@ public void stackDriverLogging() throws Exception {
             + "\"method\": \"service\"}, "
             + "\"message\": \"oops\\njava.lang.Exception: disaster\\n"
             + "	at com.google.cloud.functions.invoker.testfunctions.Log.service(Log.java:";
+
+    // TODO this test case is suspected of being flaky, as occasionally the final log entry
+    //      is missing
     TestCase exceptionTestCase =
         TestCase.builder()
             .setUrl("/?message=oops&level=severe&exception=disaster")