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.

Author: gregw

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

@@ -255,9 +255,9 @@ public void helloWorld() throws Exception {
         fullTarget("HelloWorld"),
         ImmutableList.of(
             TestCase.builder()
-                .setExpectedResponseText("hello\n")
-                .setHttpHeaders(ImmutableMap.of(
+                .setExpectedResponseHeaders(ImmutableMap.of(
                     "Content-Length", "*"))
+                .setExpectedResponseText("hello\n")
                 .build(),
             FAVICON_TEST_CASE,
             ROBOTS_TXT_TEST_CASE));